Complete Guide to TOEFL Reading Insert Sentence Questions

1. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"One major area of disagreement centers on whether these mounds were primarily ceremonial, residential, or astronomical in purpose."

Excerpt:

The earthen mounds found across the Mississippi River Valley are among the most fascinating archaeological features in North America. [■][1]. Built by various Indigenous cultures over centuries, these mounds vary widely in size, shape, and complexity, with some exceeding 30 meters in height. [■][2]. Archaeologists have studied the layout and orientation of the mounds, uncovering patterns that suggest alignment with celestial events like solstices and equinoxes. [■][3]. However, interpretations of the mounds' functions remain hotly debated. [■][4]. Some researchers argue that the mounds served as elite residences or political centers, while others believe they were built for religious ceremonies or to track astronomical phenomena.

2. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This combination of factors played a critical role in shaping the political and economic structures that would dominate the region for centuries."

Excerpt:

During the late medieval period, the Mediterranean basin was a hub of intense commercial activity and cultural exchange. Maritime republics such as Venice, Genoa, and Pisa emerged as powerful city-states, leveraging their strategic coastal positions to control trade routes connecting Europe, Asia, and Africa. [■][1] Their wealth was built upon the exchange of goods such as spices, textiles, and precious metals, which flowed through bustling ports and markets. This prosperity fueled advancements in navigation and shipbuilding, further expanding their influence across the Mediterranean Sea. [■][2] Simultaneously, these city-states developed complex political institutions, balancing oligarchic governance with emerging mercantile interests. Rivalries between these powers often led to conflicts, yet also fostered diplomatic relations and alliances. The blending of economic strength and political innovation contributed to a dynamic regional environment. [■][3] These developments had lasting impacts, influencing not only regional dominance but also the broader course of European history through trade, warfare, and cultural diffusion. [■][4]

3. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
“Although the materials and techniques used in architecture have evolved substantially, the fundamental principles of structural support remain rooted in physical laws.”

Excerpt:

Architecture has always balanced aesthetics with engineering, as builders strive to create structures that withstand environmental forces like gravity, wind, and earthquakes. [■][1]. Early constructions used natural materials such as stone, wood, and mud, each with distinct strengths and weaknesses that influenced building methods. Over time, the invention and incorporation of materials like concrete and steel enabled architects to design taller and more complex buildings, expanding creative possibilities. [■][2]. All architectural designs must comply with natural laws governing compression, tension, and bending forces to maintain stability and function. This understanding shapes decisions about building shapes, material selection, and reinforcement. [■][3]. Modern architecture incorporates computer modeling and innovative materials, yet the core engineering concepts remain consistent with those employed by ancient builders. [■][4]. Structural support systems vary, with arches distributing weight through compression along curves, and beams or cables relying on tension to bear loads such as roofs and bridges. These methods exploit different physical properties but are constrained by universal laws, enabling engineers to predict performance and ensure safety across both traditional and cutting-edge designs. Lessons from historical structures continue to influence contemporary practice, demonstrating the enduring importance of these principles. Ultimately, architects and engineers must creatively integrate scientific knowledge and artistry to achieve buildings that meet both functional requirements and aesthetic aspirations.

4. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Southern Africa was, however, relatively free of tsetse flies."

Excerpt:
As was the case elsewhere, cattle were demanding animals in Africa. They required water at least every 24 hours and large tracts of grazing grass if herds of any size were to be maintained. The secret was the careful selection of grazing land, especially in environments where seasonal rainfall led to marked differences in graze quality throughout the year. Even modest cattle herds required plenty of land and considerable mobility. To acquire such land often required moving herds considerable distances, even from summer to winter pastures. [■][1] At the same time, the cattle owners had to graze their stock in tsetse-fly-free areas. [■][2] The only protection against human and animal sleeping sickness, a disease carried by the tsetse fly, was to avoid settling or farming such areas—a constraint severely limiting the movements of cattle-owning farmers in eastern and central Africa. [■][3] As a result, small cattle herds spread south rapidly in areas where they could be grazed. [■][4] Long before cereal agriculture took hold far south of the Sahara, some hunter-gatherer groups in the savanna woodlands of eastern and southern Africa may have acquired cattle, and perhaps other domesticated animals, by gift exchange or through raids on herding neighbors.

5. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Obtaining this level of nourishment from such a harsh environment must have consumed most of Paleolithic people’s time and attention."

Excerpt:
Finally, we may doubt the notion that the Upper Paleolithic period was a paradise in which food came readily, leaving humans ample time to amuse themselves with art. [■][1] For Europe it was still the Ice Age. [■][2] An estimate of the basic level of sustenance then necessary for human survival has been judged at 2200 calories per day. [■][3] This consideration, combined with the stark emphasis upon animals in the cave art, has persuaded some archaeologists that the primary motive behind Paleolithic images must lie with the primary activity of Paleolithic people: hunting. [■][4]

6. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Some early innovations laid the groundwork for later breakthroughs, such as the development of the water wheel, which eventually influenced milling technology."

Excerpt:

The period following the Middle Ages was marked by significant technological progress across Europe and Asia. Mechanical devices, many inspired by earlier inventions from ancient civilizations, began to be refined and adapted for various uses. [■][1] Artisans and engineers improved tools and machines, increasing productivity in agriculture, manufacturing, and transportation. [■][2] Innovations such as the compass and printing press had profound effects on navigation and communication, respectively, facilitating exploration and the spread of ideas. [■][3] These technological advances contributed to economic growth and social changes, reshaping societies in fundamental ways. [■][4]

7. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The usual forms of those films relied on other ways to maintain coherence."

Excerpt:
Filmmakers began to expect that films should clearly direct the viewer’s attention, ensuring that the story unfolding onscreen was easy to follow. A growing trend emerged in which plots were structured through a chain of causes and effects—one event would clearly lead to another, often originating from a character’s motivations. In earlier cinema, however, character psychology had not played a central role. [■][1] Slapstick chase scenes or short melodramas focused more on physical comedy or familiar story setups than on psychological depth. [■][2] Increasingly after 1907, though, filmmakers began using character motivations and internal desires to explain events. [■][3] By tracking characters’ intentions and the obstacles they faced, viewers could better understand and follow the story. [■][4]

8. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Unfortunately, studies of living animals provide only a very general understanding of what various dinosaurs ate."

Excerpt:
More clues exist in other parts of the skull. The jaw joint of carnivores such as dogs and cats has the mechanical advantage of being at the same level as the tooth row, allowing the jaws to close with tremendous speed and forcing the upper teeth to occlude against the lower teeth with great precision. In herbivorous animals, rapid jaw closure is less important. Because the flat teeth of herbivores work like grindstones, however, the jaws must move both side to side and front to back. The jaw joints of many advanced herbivores, such as cows, lie at a different level than the tooth row, allowing transverse tearing, shredding, and compression of plant material. [■][1] If we extend such observations to extinct dinosaurs, we can infer dietary preferences (such as carnivory and herbivory), even though we cannot determine the exact diet. [■][2] The duck-billed dinosaurs known as hadrosaurs are a good example of a group whose jaw joint is below the level of the tooth row, which probably helped them grind up tough, fibrous vegetation.

[■][3] Paleontologists would like to be much more specific about a dinosaur’s diet than simply differentiating carnivore from herbivore. [■][4] This finer level of resolution requires direct fossil evidence of dinosaur meals. Stomach contents are only rarely preserved, but when present, allow us to determine exactly what these animals were eating.

9. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"In summary, these combined advancements and challenges have continuously influenced the trajectory of technological innovation throughout history."

Excerpt:

Technological progress has been marked by periods of rapid invention followed by phases of adaptation and refinement. Early innovations such as the wheel and the plow drastically changed daily life, allowing humans to manipulate their environment more effectively. [■][1] Subsequent developments, including the steam engine and electricity, powered industrial revolutions that transformed economies and societies on a global scale. [■][2] However, every new technology brought unforeseen obstacles, from resource depletion to social displacement, requiring societies to adjust their approaches. Governments and industries played crucial roles in supporting or hindering innovation through policy decisions and investments. [■][3] These dynamic interactions between invention, challenges, and societal responses demonstrate the complex nature of technological evolution. [■][4]

10. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?

Sentence to Insert:
"The division of time no longer reflected the organization of religious ritual."

Excerpt:
Ironically, the new machine tended to undermine Catholic Church authority. Although church ritual had sustained an interest in timekeeping throughout the centuries of urban collapse that followed the fall of Rome, church time was nature’s time. [■][1]. Day and night were divided into the same number of parts, so that except at the equinoxes, day and night hours were unequal; and then of course the length of these hours varied with the seasons. [■][2]. But the mechanical clock kept equal hours, and this implied a new time reckoning. [■][3]. The Catholic Church resisted, not coming over to the new hours for about a century. [■][4]. From the start, however, the towns and cities took equal hours as their standard, and the public clocks installed in town halls and market squares became the very symbol of a new, secular municipal authority. Every town wanted one; conquerors seized them as especially precious spoils of war; tourists came to see and hear these machines the way they made pilgrimages to sacred relics.

11. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This streaking phenomenon is called a meteor or sometimes a falling star or shooting star."

Excerpt:
A comet leaves a trail of matter behind it as it moves through the inner solar system. Some of this debris may get strewn across Earth's orbit around the Sun.[■][1] When Earth passes through this part of its annual path, it sweeps through the dust trail.[■][2] The particles enter Earth's atmosphere at high velocity.[■][3] The air friction can cause one of these bits of matter to produce a brief streak of light as it burns up in the atmosphere.[■][4]

12. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Thousands of clay writing tablets from the Near East have been preserved by being baked in this way."

Excerpt:
Human destruction of the archaeological record might be caused by burials of the kind just described being dug into earlier deposits. But people in the past deliberately or accidentally obliterated traces of their predecessors in innumerable other ways. Rulers often destroyed monuments or erased inscriptions belonging to previous chiefs or monarchs. [■][1] On the other hand, some human destruction meant to obliterate has inadvertently preserved material for the archaeologist to find. [■][2] Burning, for example, may not always destroy. [■][3] Clay daubing and adobe usually decay, but if a structure has been burned, the mud is baked to the consistency of a brick. [■][4]

13. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Even the air space within the tiles served to insulate the metal from the heat of fire."

Excerpt:
From the standpoint of real estate developers, the purpose of skyscrapers was to increase rental space in valuable urban locations. But to create usable high-rise buildings, a number of technical challenges needed to be solved. One problem was getting people to the upper floors, since after five or six stories it becomes exhausting to climb stairs. Updated and electrified versions of the freight elevator that had been introduced by Elish Graves Otis in 1853 (several decades before skyscraper construction) solved this problem. Another issue was fire safety. The metal supporting buildings became soft when exposed to fire and collapsed relatively quickly. (They could melt at 2,700 Fahrenheit, whereas major fires achieve temperatures of 3,000 degrees). However, when the metal is encased in fire-retardant materials, its vulnerability to fire is much decreased. [■][1] In Chicago, a system was developed for surrounding the metal components with hollow tiles made from brick-like terra-cotta. [■][2] Such tiles are impervious to fire. [■][3] The terra-cotta tiles were used both to encase the supporting members and as flooring. [■][4] A structure built with steel beams protected by terra-cotta tiles was still three times lighter than a comparably sized building that used masonry construction, so the weight of the tiles was not a problem.

14. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This development occurred primarily for two reasons."

Excerpt:
The assemblies of American colonial representatives were more democratic. [■][1] Although every colony had property qualifications for voting, probably the great majority of adult white males owned enough land to meet them. [■][2] Moreover, the system for apportioning representation was more balanced. [■][3] New England colonies gave every town the right to send delegates to the legislature. [■][4] Outside New England, the unit of representation was usually the county. The political organization of new counties and the extension of representation seldom kept pace with the rapid advance of settlement westward, but nowhere was representation so uneven or irrational as in England.

15. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Clearly, a more plausible mechanism was needed to explain how stars generate energy."

Excerpt:
Until the early- to mid-twentieth century, scientists believed that stars generate energy by shrinking. [■][1] As stars contracted, it was thought, they would get hotter and hotter, giving off light in the process. [■][2] This could not be the primary way that stars shine, however. [■][3] If it were, they would scarcely last a million years, rather than the billions of years in age that we know they are. [■][4] We now know that stars are fueled by nuclear fusion. Each time fusion takes place, energy is released as a by-product. This energy, expelled into space, is what we see as starlight. The fusion process begins when two hydrogen nuclei smash together to form a particle called the deuteron (a combination of a positive proton and a neutral neutron). Deuterons readily combine with additional protons to form helium. Helium, in turn, can fuse together to form heavier elements, such as carbon. In a typical star, merger after merger takes place until significant quantities of heavy elements are built up.

16. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Although people did not read widely, or extensively, they read intensively so as to thoroughly understand the limited number of books that were available for reading."

Excerpt:
Cheap print was not entirely unprecedented. In seventeenth- and eighteenth- century England and France, cheap collections of stories, ballads, and other miscellany had circulated among the lower classes. But since only a minority of the poor could read, most listened while a few read aloud; thus cheap print reached not so much a reading as a listening public. The expansion of cheap print in the nineteenth century in America and Europe was on a much larger scale, and it took place during a great increase in popular literacy. Together these amounted to a cultural watershed. [■][1] Traditionally, even in literate homes, books and other publications had been relatively rare and treasured objects; reading meant returning to a few texts, especially religious works. [■][2] But with the explosion of print, reading became more varied, and readers scanned newspapers, magazines, and cheap books that they soon passed on or discarded. [■][3] Intensive reading of religious and other works did not disappear, but reading became an increasingly common form of diversion as well as devotion. [■][4]

17. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This insight prompted scientists to revise earlier assumptions about the pace and pattern of early human expansion."

Excerpt:

Genetic evidence has played a crucial role in tracing the migration of early Homo sapiens out of Africa. [■][1] By analyzing mitochondrial DNA from present-day populations, researchers have reconstructed the likely paths taken by human groups as they spread across the globe. [■][2] A surprising discovery emerged when DNA from ancient remains in Southeast Asia revealed older-than-expected settlement dates. [■][3] These findings suggested that early humans may have reached remote regions of the continent far earlier than traditional archaeological models had indicated. [■][4]

18. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"In other words, lizard tongues are forked precisely in cases where being able to follow odor trails is an advantage."

Excerpt:
Several kinds of evidence support the hypothesis that forked tongues evolved as chemosensory edge detectors to enhance the ability to follow odor trails: Snakes and lizards spread the tines of their tongue apart when they retrieve odor molecules, then draw the tines together when retracting the tongue. The greater the distance between sampling points, the better the animals sample differences within an odor trail. [■][1] Lizards that forage widely have forked tongues, whereas lizard species without forked tongues tend not to forage widely. [■][2] Forked tongues have evolved independently at least twice in different families of reptiles, indicating their value as an adaptation. [■][3] ln the snake nervous system, each tine of the tongue is linked to a nucleus in the other side of the brain, and the two nuclei are linked across the two hemispheres. This arrangement is similar to the anatomy of auditory centers in mammals and birds that permits the computation of differences between what one ear hears and what the other ear hears and thus mediates auditory localization. [■][4]

19. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"If not through the walls or its pores, how does oxygen enter the nest at all, since the nest has a closed surface?"

Excerpt:
But how is this well-insulated nest ventilated? Its many occupants require over 250 quarts of oxygen (more than 1,200 quarts of air) per day. How can so much oxygen diffuse through the thick walls of the mound? [■][1] Even the pores in the wall are filled with water, which almost stops the diffusion of gases. [■][2] The answer lies in the construction of the nest. [■][3] The interior consists of a large central core in which the fungus is grown, below it is a “cellar” of empty space, above it is an “attic” of empty space, and within the ridges on the outer wall of the nest, there are many small tunnels that connect the cellar and the attic. [■][4] The warm air in the fungus gardens rises through the nest up to the attic. From the attic, the air passes into the tunnels in the ridges and flows back down to the cellar. Gases, mainly oxygen coming in and carbon dioxide going out, easily diffuse into or out of the ridges, since their walls are thin and their surface area is large because they protrude far out from the wall of the mound. Thus air that flows down into the cellar through the ridges is relatively rich in oxygen, and has lost much of its carbon dioxide. It supplies the nest’s inhabitants with fresh oxygen as it rises through the fungus-growing area back up to the attic.

20. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"There is ongoing disagreement among scholars about whether this transition was primarily a result of environmental pressures or cultural innovations."

Excerpt:

The Neolithic Revolution marks one of the most profound transformations in human history, representing the shift from hunting and gathering to agriculture and settlement. [■][1]. Beginning around 12,000 years ago in different regions of the world, humans started domesticating plants and animals, leading to more stable food supplies and the growth of permanent villages. [■][2]. This transition allowed for population increases and the development of complex social structures, including trade networks, specialized labor, and governance systems. [■][3]. However, the exact causes and pace of the Neolithic Revolution vary between regions, and many factors likely played interrelated roles. [■][4]. Some scholars emphasize environmental changes such as climate warming that made agriculture feasible, while others point to human creativity and experimentation as the driving force behind this shift. The debate over these influences continues as new archaeological discoveries provide additional insights into early farming communities and their interactions with the surrounding environment.

21. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The innovations introduced in agriculture dramatically transformed human society, but the underlying challenges of soil fertility, water management, and crop sustainability persisted and shaped farming practices across cultures."

Excerpt:

Agriculture began independently in various regions around the world, marking a major turning point from nomadic lifestyles to settled communities. Early farmers domesticated plants and animals, selecting species that provided reliable food sources. These developments led to population growth, social stratification, and the rise of cities. [■][1] Over time, techniques such as crop rotation, irrigation, and fertilization were developed to increase yields and address environmental limitations. The use of tools evolved from simple digging sticks to advanced plows powered by animals, enhancing efficiency. [■][2] Although these technological and social changes were significant, farmers across regions faced ongoing obstacles related to maintaining soil health, conserving water, and ensuring long-term sustainability. These persistent challenges required adaptive strategies that reflected both local environmental conditions and cultural knowledge. [■][3] In some societies, agricultural innovations fueled trade and wealth, while in others, farming difficulties contributed to societal stress and migration. [■][4] Modern agriculture continues to build on this legacy, balancing productivity with environmental concerns through scientific research and technological advancements.

22. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These incremental innovations laid the foundation for more complex machinery, eventually transforming industrial manufacturing processes."

Excerpt:

During the early stages of the Industrial Revolution, simple machines and mechanical devices began to change the landscape of manufacturing. Artisans and engineers built upon centuries-old knowledge, gradually refining tools such as the spinning wheel and water-powered mills to improve efficiency and output. [■][1] These machines, although rudimentary by modern standards, enabled producers to increase their production capacity beyond what manual labor alone could achieve. This period also saw improvements in metallurgy, which provided stronger materials to build more durable and effective machines. [■][2] Workshops transformed into factories as mechanized processes began to replace handcrafting, leading to specialization of labor and the creation of new jobs related to machine operation and maintenance. Despite their relatively simple design, these early innovations were crucial in accelerating productivity and shaping the path of industrialization. [■][3] However, many machines required frequent repair and skilled oversight, which limited their initial impact on mass production. Over time, engineers developed more reliable and intricate devices, laying the groundwork for the large-scale factories and assembly lines that defined later industrial society. [■][4]

23. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Practical and unimpressive, most were barely taller than the average adult."

Excerpt:
This art had a major impact on the native peoples, and one of the most important factors was a change in the scale of buildings. Pre-Roman Britain was highly localized, with people rarely traveling beyond their own region. On occasion large groups amassed for war or religious festivals, but society remained centered on small communities. Architecture of this era reflected this with even the largest of the fortified towns and hill forts containing no more than clusters of medium-sized structures. The spaces inside even the largest roundhouses were modest, and the use of rounded shapes and organic building materials gave buildings a human scale. [■][1] But the effect of Roman civil architecture was significant. The sheer size of space enclosed within buildings like the basilica of London must have been astonishing. [■][2] This was an architecture of dominance in which subject peoples were literally made to feel small by buildings that epitomized imperial power. [■][3] Supremacy was accentuated by the unyielding straight lines of both individual buildings and planned settlements since these too provided a marked contrast with the natural curvilinear shapes dominant in the native realm. [■][4]

24. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?

Sentence to Insert:
"That is because residents of a city did not usually discard used pottery at the same site over a long period of time."

Excerpt:
[■][1]. Only rarely can we derive any “real” quantities from deposits of broken pots. [■][2]. However, there is one exceptional dump, which does represent a very large part of the site’s total history of consumption and for which an estimate of quantity has been produced. [■][3]. On the left bank of the Tiber River in Rome, by one of the river ports of the ancient city, is a substantial hill some 50 meters high called Monte Testaccio. [■][4]. It is made up entirely of broken oil amphorae, mainly of the second and third centuries A.D. It has been estimated that Monte Testaccio contains the remains of some 53 million amphorae, in which around 6,000 million liters of oil were imported into the city from overseas. Imports into imperial Rome were supported by the full might of the state and were therefore quite exceptional—but the size of the operations at Monte Testaccio, and the productivity and complexity that lay behind them, nonetheless cannot fail to impress. This was a society with similarities to modern ones—moving goods on a gigantic scale, manufacturing high-quality containers to do so, and occasionally, as here, even discarding them on delivery.

25. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The interplay between resource availability and technological response has been a driving force in shaping societal structures throughout history."

Excerpt:

Human societies have continuously adapted to their natural surroundings by developing tools and strategies to exploit available resources. Early communities utilized simple stone tools and foraging techniques, which limited population size and settlement stability. [■][1] With the advent of agriculture, humans began to manipulate their environment more intensively, cultivating crops and domesticating animals to support larger populations. [■][2] Technological innovations such as irrigation systems and plows enabled more efficient food production, but also required organizational changes to manage labor and resources. [■][3] These shifts not only influenced economic activity but also altered social hierarchies and governance, as communities adapted to meet the demands of increased complexity. [■][4]

26. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"If the Mississippi River were not contained by such systems, it would probably abandon its present path and cut into the channel of a nearby river to the west."

Excerpt:
A stream also slows abruptly where it enters the still water of a lake or ocean. The sediment settles out to form a nearly flat landform called a delta. Part of the delta lies above water level, and the remainder lies slightly below water level. Deltas are commonly fan-shaped, resembling the Greek letter “delta” (Δ). Both deltas and alluvial fans change rapidly. Sediment fills channels (waterways), which are then abandoned while new channels develop as in a braided stream. As a result, a stream feeding a delta or fan splits into many channels called distributaries. A large delta may spread out in this manner until it covers thousands of square kilometers. [■][1] Most fans, however, are much smaller, covering a fraction of a square kilometer to a few square kilometers. [■][2] The Mississippi River has flowed through seven different delta channels during the past 5,000 to 6,000 years. [■][3] But in recent years, engineers have built great systems of levees (retaining walls) in attempts to stabilize the channels. [■][4]

27. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Existing theories about the early atmosphere were used to help design the study."

Excerpt:
A little over 3.8 billion years ago is widely accepted as the approximate time life began on Earth. However, how life originated remains uncertain. There is no single accepted theory—rather, there are numerous competing ideas, each addressing the question from a different perspective. [■][1] This marks a shift from the situation in 1953, when a groundbreaking experiment on the origin of life was published. At that time, Stanley Miller and Harold Urey had just completed their renowned laboratory simulation of early Earth conditions at the University of Chicago. [■][2] In their experiment, they passed electrical sparks—representing lightning—through a mixture of methane, ammonia, and hydrogen gases above a pool of boiling water, simulating the early ocean. [■][3] As a result, a reddish substance rich in amino acids collected in their apparatus. Amino acids, when linked together in long, folded chains, form proteins—fundamental components of living cells. [■][4] The spontaneous creation of amino acids suggested that the leap to the spontaneous origin of life might not be so far-fetched after all.

28. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This mechanism is believed to be responsible for the seasonal migration patterns observed in many bird species."

Excerpt:

Birds use a variety of cues to navigate during migration, including the position of the sun, stars, and Earth's magnetic field. [■][1] Research has shown that specialized cells containing magnetite particles in birds’ upper beaks may act as biological compasses. [■][2] These magnetite-based receptors can detect subtle changes in the magnetic field, allowing birds to orient themselves even under cloudy skies. [■][3] However, the exact neural pathways that translate magnetic information into directional movement are still not fully understood. [■][4] Understanding these navigation systems is crucial for conserving migratory species facing environmental challenges.

29. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"But their origin and evolution have been under considerable dispute."

Excerpt:
What type of plant was the ancestor to the angiosperms? Most botanists now agree that flowering plants originated from a single evolutionary line, meaning they are monophyletic. [■][1] Some paleontologists have proposed that cycads—tropical, palmlike plants—might represent the ancestral form. [■][2] Others argue that flowering plants may have evolved from ancient seed-bearing ferns. [■][3] Still others point to morphological features in primitive modern plants that resemble those of present-day pines. [■][4] The true evolutionary history of angiosperms remains uncertain.

30. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These pigments helped scientists trace the types of plants that ancient populations might have used in rituals or daily consumption."

Excerpt:

Archaeologists studying ceramic shards from pre-Columbian South American sites have discovered microscopic residues that offer insight into the cultural practices of early civilizations. [■][1] Among these residues were plant-based pigments used in decorating pottery or possibly even for ceremonial purposes. [■][2] The pigments, when analyzed using high-resolution mass spectrometry, revealed chemical markers linked to species such as achiote and purple yam. [■][3] These findings not only help date the artifacts but also give clues about ancient trade routes, as some plants were not native to the region. [■][4] In this way, even tiny pigment particles can become powerful tools for reconstructing social behavior and interaction in prehistoric societies.

31. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Leaf design, then, is valuable in moisture retention, but it is not the only effective strategy."

Excerpt:
Around 140 species of grasses naturally occur in the arid Great Plains grasslands of North America. One key to the prairie grasses' success is their ability to conserve water in a dry environment. Like most plants, grasses take in water through their roots and lose it as water vapor through tiny mouth-shaped valves, or stomata, in their leaves. The larger the surface of the leaf and the more stomata it bears, the greater the risk that the plant will lose too much moisture through evaporation and collapse.[■][1] Grasses are protected from this trauma by having a reduced number of stomata and by the design of their leaves, which take the form of narrow blades.[■][2] What's more, the surfaces of these reduced leaves are often modified-corrugated with ridges or covered in hairs-so that the wind can't sweep across the surface and draw out moisture.[■][3] The roughened surface holds a thin layer of humid air next to the leaf and thus helps to reduce the "evaporative demand," or drying power, of the atmosphere.[■][4] Some grasses, including western wheatgrass, June grass, and blue grama, roll up the edges of their leaves during times of drought to help keep their tissues from drying out.

32. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The location of these heaps of rubbish can be an accurate indicator of earlier coastlines."

Excerpt:
[■][1] Raised beaches often consist of areas of sand, pebbles, or dunes, sometimes containing seashells or piles of debris comprising shells and bones of marine animals used by humans. [■][2] In Tokyo Bay, for example, shell mounds of the Jomon period (about 10,000 to 300 B.C.E.) mark the position of the shoreline at a time of maximum inundation by the sea (6,500–5,500 years ago), when, through tectonic movement, the sea was three to five meters higher in relation to the contemporary landmass of Japan than at present. [■][3] Analysis of the shells themselves has confirmed the changes in marine topography, for it is only during the maximum phase that subtropical species of mollusc are present, indicating a higher water temperature. [■][4]

33. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
“Despite significant advancements in communication technologies, the fundamental need to convey clear and reliable information remains unchanged.”

Excerpt:

Communication has been an essential aspect of human society since its earliest days, facilitating the sharing of knowledge, culture, and emotions across distances. [■][1]. Early methods included spoken language, gestures, and primitive symbols, which gradually evolved into more complex written forms. The invention of the printing press in the 15th century revolutionized information dissemination by making texts widely accessible. [■][2]. In the 19th and 20th centuries, telegraphy and telephony further expanded the reach and speed of communication, connecting individuals across vast geographic areas. The digital age has introduced computers, the internet, and mobile devices, enabling instantaneous global interactions. [■][3]. Despite these technological leaps, challenges such as signal interference, misinterpretation, and information overload continue to affect communication quality. [■][4]. Scholars and engineers focus on improving the clarity, efficiency, and security of communication channels, ensuring that information remains accurate and meaningful regardless of the medium used.

34. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Experts continue to debate whether this innovation was primarily driven by practical needs or social and cultural factors."

Excerpt:

The invention of pottery represents a major milestone in human history, marking a shift toward more sedentary lifestyles and complex societies. [■][1]. Pottery fragments have been found at archaeological sites dating back over 10,000 years, indicating the early development of this craft in diverse regions such as East Asia, the Middle East, and the Americas. [■][2]. Early pottery was often simple in form and function, used mainly for storing food and water, cooking, or fermenting beverages. [■][3]. Over time, potters refined their techniques, introducing decorative elements and experimenting with different firing methods to improve durability and aesthetic appeal. [■][4]. These advancements reflect both technological progress and changing social dynamics, as pottery increasingly took on symbolic and ritual significance in many cultures.

35. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This theory gained traction after several archaeological discoveries suggested that early humans might have engaged in complex symbolic behaviors much earlier than previously believed."

Excerpt:

For much of the twentieth century, it was widely accepted that the emergence of symbolic thought—expressed through art, language, and ritual—marked a sudden leap in human cognitive evolution approximately 40,000 years ago. [■][1] However, recent findings have challenged this timeline, revealing artifacts that indicate symbolic behavior in human ancestors dating back over 100,000 years. [■][2] These include engraved objects, ochre use, and evidence of burial practices, all suggesting a rich cultural life much earlier than the so-called "cognitive revolution." Despite some skepticism, this new perspective has led researchers to reconsider how and when complex cognition developed. [■][3] The debate continues as scientists analyze new data and develop theories that integrate archaeological, genetic, and anthropological evidence. [■][4] Understanding the origins of symbolic thought is crucial for grasping the unique nature of human intelligence and social organization.

36. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"One notable drawback of this technique is its inability to detect molecules that are present in extremely low concentrations."

Excerpt:

Gas chromatography has become an essential tool in analytical chemistry for separating and identifying compounds in complex mixtures. [■][1] In this method, a sample is vaporized and carried by an inert gas through a column coated with a liquid or polymer. [■][2] As compounds move through the column, they interact differently with the coating, allowing them to separate based on chemical properties. [■][3] The separated compounds then pass through a detector, which measures their retention times and helps identify them. Despite its precision and widespread use, gas chromatography is not without limitations. [■][4]

37. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Such developments reveal how incremental technological improvements often build upon previous knowledge, paving the way for transformative inventions."

Excerpt:

The evolution of printing technology exemplifies the gradual progression of innovation that has significantly shaped human communication. Early printing methods, such as woodblock printing developed in East Asia, allowed for the mass reproduction of texts but were limited in flexibility and efficiency. [■][1] In the 15th century, Johannes Gutenberg introduced movable type printing in Europe, revolutionizing the production of books by dramatically increasing speed and reducing costs. This breakthrough facilitated the spread of knowledge, literacy, and scientific ideas, contributing to the Renaissance and Reformation movements. [■][2] Following Gutenberg’s invention, printing technologies continued to evolve, incorporating steam power and mechanization during the Industrial Revolution, which further enhanced printing capacity and accessibility. [■][3] These continuous improvements not only impacted publishing but also influenced education, politics, and culture by making information widely available to diverse populations. The trajectory of printing technology highlights the importance of building upon earlier achievements to create powerful new tools that transform societies. [■][4]

38. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These advantages make it an ideal candidate for use in biomedical implants and next-generation electronics."

Excerpt:

Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, has captured the attention of scientists and engineers worldwide. [■][1]. One of its most remarkable properties is its strength—graphene is over 100 times stronger than steel while remaining extremely lightweight. [■][2]. In addition, it conducts electricity more efficiently than copper and is nearly transparent, allowing it to be used in touchscreens, solar cells, and flexible electronics. [■][3]. Researchers are especially interested in its biocompatibility, which means it can safely interact with human tissues without causing immune reactions. [■][4]. However, despite its promise, large-scale production of high-quality graphene remains a major challenge.

39. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Together, these factors highlight the complex interplay between technology, environment, and society that has continuously shaped human development."

Excerpt:

Human civilizations have long depended on technology to manipulate their environments and improve living conditions. Innovations such as irrigation systems, metallurgy, and transportation networks facilitated the expansion of cities and trade. [■][1] Environmental factors, including climate variations and resource availability, often dictated the success or failure of societies. Some civilizations adapted by developing new agricultural methods or relocating, while others declined. [■][2] Social structures, such as governance and economic organization, also influenced how communities responded to challenges. Hierarchical systems could mobilize resources efficiently, but they sometimes fostered inequality and unrest. [■][3] These diverse elements interacted in ways that shaped historical trajectories, demonstrating the interconnected nature of human progress and its dependence on multiple dynamic forces. [■][4] Understanding this complex relationship is essential for interpreting past civilizations and addressing contemporary global challenges.

40. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This design allowed the mechanical energy from the falling weight to be transferred smoothly and continuously to the rotating shaft."

Excerpt:

The flyball governor, an early example of an automatic control device, was invented during the Industrial Revolution to regulate the speed of steam engines. [■][1] It used a set of spinning metal balls attached to a vertical spindle, which rose or fell in response to the engine’s speed. [■][2] If the engine spun too quickly, centrifugal force caused the balls to rise and adjust a valve, reducing the steam flow and slowing the engine. [■][3] One key component of this system was the linkage between the governor and the throttle valve, which had to be finely tuned to maintain consistent engine performance. [■][4] The flyball governor not only represented a milestone in mechanical engineering, but it also laid foundational principles for later developments in automation and feedback systems.

41. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"While considerations of political power and ease of administration were decisive in choosing the location of the new capital, the site clearly had other advantages."

Excerpt:
[■][1] The region of Memphis must have also served as an important node for transport and communications, even before the unification of Egypt. [■][2] The region probably acted as a conduit for much, if not all, of the river-based trade between northern and southern Egypt. [■][3] Moreover, commodities (such as wine, precious oils, and metals) imported from the Near East by the royal courts of predynastic Upper Egypt would have been channeled through the Memphis region on their way south. [■][4] In short, therefore, the site of Memphis offered the rulers of the Early Dynastic Period an ideal location for controlling internal trade within their realm, an essential requirement for a state-directed economy that depended on the movement of goods.

42. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The resulting difference in atmospheric pressure between the city and the countryside can cause air to shift."

Excerpt:
On clear still nights when the heat island is pronounced, a small thermal low-pressure area forms over the city. [■][1] Sometimes a light breeze—called a country breeze—blows from the countryside into the city. [■][2] If there are major industrial areas along the outskirts, pollutants are carried into the heart of town, where they tend to concentrate. [■][3] Such an event is especially probable if vertical mixing and dispersion of pollutants are inhibited. [■][4] Pollutants from urban areas may even affect the weather downwind from them.

43. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These distinctive vocalizations serve multiple purposes, from establishing territory to attracting mates and warning of potential dangers."

Excerpt:

Bird communication is a complex behavior involving a variety of sounds, calls, and songs. [■][1] Many bird species have evolved unique vocal repertoires that allow them to convey specific messages to others within their group or to deter intruders. [■][2] The structure and frequency of these sounds can vary widely, with some species capable of producing songs that last several minutes and include numerous distinct notes. [■][3] Moreover, vocal learning—the ability to modify and acquire new sounds—is present in only a few bird groups, such as songbirds and parrots, which contributes to the diversity of bird communication across different habitats. [■][4] In addition to vocalizations, birds also use visual signals like feather displays and body postures to communicate, highlighting the multifaceted nature of avian interaction. Understanding these communication systems is important for conservation efforts, as changes in habitat can disrupt these critical behaviors.

44. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These additions often cause the volcano to bulge out sideways."

Excerpt:
Active volcanoes expand in volume as they acquire new supplies of magma from below. [■][1] As a result, an increase in the steepness or bulging of a volcano's slope may signal an impending eruption. [■][2] To detect the inflation of a volcanic cone, a tilt meter, a device like a carpenter's level, is used. [■][3] As magma rises, it pushes aside fractured rock, enlarging the fractures as it moves. Because this type of fracturing causes earthquakes, eruptions are often preceded by a distinctive pattern of earthquake activity called harmonic tremors, a continuous rhythmic rumbling. [■][4] Sensitive equipment that monitors the location where these tremors occur can measure the increased height of rising magma. The rate at which the magma rises provides an estimate of when an eruption may occur. Indeed, it served as the principal​​​​​​​ means by which scientists accurately predicted recent eruptions of Mount St. Helens.

45. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Venus may not have always been this way."

Excerpt:
Venus and Earth are commonly regarded as twin planets but not identical twins. They are about the same size, are composed of roughly the same mix of materials, and may have been comparably endowed at their beginning with carbon dioxide and water. However, the twins evolved differently, largely because of differences in their distance from the Sun. With a significant amount of internal heat, Venus may continue to be geologically active with volcanoes, rifting, and folding. [■][1] However, it lacks any sign of a hydrologic system (water circulation and distribution): there are no streams, lakes, oceans, or glaciers. [■][2] Space probes suggest that Venus may have started with as much water as Earth, but it was unable to keep its water in liquid form. [■][3] Because Venus receives more heat from the Sun, water released from the interior evaporated and rose to the upper atmosphere where the Sun’s ultraviolet rays broke the molecules apart. [■][4] Much of the freed hydrogen escaped into space, and Venus lost its water. Without water, Venus became less and less like Earth and kept an atmosphere filled with carbon dioxide. The carbon dioxide acts as a blanket, creating an intense greenhouse effect and driving surface temperatures high enough to melt lead and to prohibit the formation of carbonate minerals. Volcanoes continually vented more carbon dioxide into the atmosphere. On Earth, liquid water removes carbon dioxide from the atmosphere and combines it with calcium, from rock weathering, to form carbonate sedimentary rocks. Without liquid water to remove carbon from the atmosphere, the level of carbon dioxide in the atmosphere of Venus remains high.

46. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Such a system was clearly awkward for large inventories."

Excerpt:
And not only of literacy, but numeracy (the representation of quantitative concepts) as well. The evidence of the tokens provides further confirmation that mathematics originated in people’s desire to keep records of flocks and other goods. Another immensely significant step occurred around 3100 B.C. E., when Sumerian accountants extended the token-based signs to include the first real numerals. [■][1] Previously, units of grain had been represented by direct one-to-one correspondence—by repeating the token or symbol for a unit of grain the required number of times. [■][2] The accountants, however, devised numeral signs distinct from commodity signs, so that eighteen units of grain could be indicated by preceding a single grain symbol with a symbol denoting “18.” [■][3] Their invention of abstract numerals and abstract counting was one of the most revolutionary advances in the history of mathematics. [■][4]

47. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"In fact, some of these colonies have been known to last for several centuries."

Excerpt:
Individual corals are known as coral polyps; each is a single animal. [■][1] In isolation a coral polyp looks very similar to a sea anemone, but unlike sea anemones, which live separated from each other, corals form colonies. [■][2] A few species remain solitary, but in most cases, new polyps bud off the initial founding polyp, and gradually colonies of thousands or even millions of polyps will grow, each connected to its neighbors by living tissue. [■][3] Freed from the limitations of living alone, colonies can grow to immense sizes and live a very long time. [■][4]

48. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Scientists have long debated whether this sudden change was triggered by environmental shifts or by internal social dynamics."

Excerpt:

The collapse of the Roman Empire remains one of history's most studied and discussed events. [■][1] Spanning centuries, the empire grew to encompass vast territories across Europe, North Africa, and the Middle East, with a complex system of governance and infrastructure. [■][2] In the 4th and 5th centuries CE, a series of military defeats, economic troubles, and internal strife gradually weakened Roman control. [■][3] The traditional narrative focuses on invasions by barbarian tribes as the primary cause, but more recent studies have highlighted factors such as political corruption, economic inflation, and declining civic engagement. [■][4] Today, historians acknowledge that the empire's fall was likely the result of multiple intertwined causes rather than a single event.

49. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This means that such birds can navigate with remarkable precision even in total darkness or during overcast conditions."

Excerpt:

Bird migration is a complex behavior involving multiple navigational systems. [■][1]. While many birds rely on visual cues such as landmarks and the position of the sun or stars, others use internal compasses that respond to Earth’s magnetic field. [■][2]. Specialized cells containing magnetite—a magnetic mineral—are located in the upper beaks of some bird species, allowing them to sense magnetic field lines and detect subtle shifts in orientation. [■][3]. This biological compass operates independently of light conditions, making it particularly useful when other cues are unavailable. [■][4]. Researchers are still uncovering how birds integrate magnetic information with other sensory input, such as smell and polarized light, to form a complete map of their migratory routes.

50. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?

Sentence to Insert:
"They believe that environmental conditions may play a crucial role in determining which of the two modes will be in operation over a given period."

Excerpt:
[■][1]. Similar exhaustive studies are required for many different kinds of organisms from many different periods. [■][2]. Most researchers expect to find that both modes of transition from one species to another are at work in evolution. [■][3]. Slow, continuous change may be the norm during periods of environmental stability, while rapid evolution of new species occurs during periods of environmental stress. [■][4]. But a lot more studies like Sheldon’s are needed before we can say for sure.

51. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Some sleighs were capable of carrying over 100 tons worth of timber."

Excerpt:
For industrial lumbering to thrive, loggers had to overcome the seasonal limitations that affected productivity. Traditionally, trees were cut during the winter, when snow and ice made it easier to haul logs on sleds or sleighs to nearby streams. Once the water thawed in spring, workers would float the logs downstream to sawmills for processing during the warmer months. [■][1]. If the weather didn’t cooperate—say, if the winter was too warm or dry, or the spring thaw came too late—production could fall behind. To reduce their dependence on natural conditions, lumber workers developed new methods of moving logs out of forests. [■][2]. In the 1870s, loggers in the Great Lakes region began spraying water on sleigh roads to form an artificial layer of ice and improve travel conditions. [■][3]. The ice helped lower friction, enabling sleighs to carry heavier loads more efficiently. [■][4].

52. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Each mineral has an orderly arrangement of atoms (crystalline structure) and a definite chemical composition that give it a unique set of physical properties."

Excerpt:
A mineral is a naturally occurring solid formed by inorganic processes.[■][1] Since the internal structure and chemical composition of a mineral are difficult to determine without the aid of sophisticated tests and apparatus, the more easily recognized physical properties are used in identification.[■][2]

Most people think of a crystal as a rare commodity, when in fact most inorganic solid objects are composed of crystals.[■][3] The reason for this misconception is that most crystals do not exhibit their crystal form: the external form of a mineral that reflects the orderly internal arrangement of its atoms.[■][4] Whenever a mineral forms without space restrictions, individual crystals with well-formed crystal faces will develop. Some crystals, such as those of the mineral quartz, have a very distinctive crystal form that can be helpful in identification. However, most of the time, crystal growth is interrupted because of competition for space, resulting in an intergrown mass of crystals, none of which exhibits crystal form.

53. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The speed and simplicity of this process are especially useful in emergency situations where diagnostic speed is critical."

Excerpt:

Polymerase Chain Reaction (PCR) has revolutionized molecular biology by allowing scientists to amplify tiny quantities of DNA in a short time. [■][1]. This technique uses cycles of heating and cooling to replicate a targeted DNA segment millions of times, often completing the process within just a few hours. [■][2]. PCR has enabled advances in fields ranging from forensic science to infectious disease monitoring. [■][3]. For instance, doctors can now detect viral genetic material in a patient's sample even before symptoms appear, allowing earlier treatment and isolation measures. [■][4]. Since its invention in the 1980s, PCR has continued to evolve, with newer variants offering greater precision and speed.

54. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These functions are tightly integrated and often depend on coordinated activity among multiple regions."

Excerpt:

The human brain is a remarkably complex organ composed of billions of neurons organized into specialized regions. [■][1] Each of these regions is associated with specific functions such as processing visual input, regulating movement, or managing emotions. [■][2] For example, the occipital lobe handles vision, the frontal lobe is involved in decision-making, and the amygdala helps process emotional reactions. [■][3] While these regions can be identified anatomically, they rarely operate in isolation. [■][4] Brain imaging studies have revealed that even the simplest task activates a network of regions working together to produce thought, perception, or action.

55. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"As a result, less energy will be needed to produce a crop of seeds large enough to flood the reduced market for them."

Excerpt:
Producing a large quantity of seeds requires a great deal of energy—so much that pinyon pine trees likely cannot sustain such output every year. More importantly, it would actually be harmful for the trees to do so even if they could. Constant seed abundance would make the supply predictable, allowing seed predators to increase steadily over time, potentially to the point of consuming nearly every seed. Instead, it is more adaptive for the trees to produce massive seed crops only occasionally. [■][1]. This strategy offers several important benefits. First, energy can be stored over multiple years and then allocated to cone and seed production, ensuring enough resources to generate a sizable seed crop. [■][2]. Second, predator populations—such as birds and small mammals—decline in years when few seeds are available, whether due to starvation, fewer offspring, or migration. [■][3]. Pinyon pines in most regions tend to have major seed crop years approximately every six years. [■][4].

56. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This large-scale agriculture has actually resulted in a decrease in biological diversity."

Excerpt:
Three phenomena have characterized the more recent impact of agriculture on Earth. [■][1] The first was the increase in human population, which has doubled at shorter and shorter intervals over the last thousand years. [■][2] The result was increased acreage under cultivation and a fundamental remodeling of the globe toward managed rather than wild ecosystems. [■][3] By 1998 there were 3,410,523,800 acres of land under cultivation worldwide, an area larger than the United States. [■][4] Entire ecosystems have disappeared, others remain but are threatened, and the sheer volume of people and area of farmland have been major forces of biological change.

57. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"In time, their efforts to transform the new countryside and make it more productive succeeded."

Excerpt:
[■][1] In contrast, the European colonists who intruded on this harmonious world often viewed it as alien and menacing; some called it, in the language of the Bible, a "howling wilderness." [■][2] The newcomers to America brought with them agricultural practices and preconceptions about nature based on their experiences in England. [■][3] They saw uncultivated lands as "wastes" that needed to be "broken," "dressed," and "improved." In New England, transplanted English settlers attempted to subdue what they considered a fearsome wilderness by mapping the countryside, draining marshlands, clearing pastures, fencing particular parcels, and planting wheat and other familiar crops. [■][4] Within twenty years of the initial Puritan settlement, Edward Johnson boasted of the newcomers' achievements: "This remote, rocky, barren, bushy, wild-woody wilderness, a receptacle for lions, wolves, bears, foxes, raccoons…, beavers, otters, and all kind of wild creatures, a place that never afforded the Natives better than the flesh of a few wild creatures and parched Indian corn inched out with chestnuts and bitter acorns, now through the mercy of Christ [has] become a second England for fertility in so short a space, that it is indeed the wonder of the world."

58. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This phenomenon, known as social buffering, has been observed in both laboratory settings and natural environments."

Excerpt:

In the field of animal behavior, researchers have long been interested in the ways social relationships influence an individual’s physiological response to stress. [■][1] Numerous studies have shown that animals housed in isolation tend to exhibit elevated stress markers such as increased cortisol levels and heightened heart rates. By contrast, those living in stable social groups generally demonstrate more stable physiological profiles, even when exposed to identical environmental stressors. [■][2] These effects are not limited to primates; rodents, birds, and even some fish species have shown similar trends in stress reduction through companionship. In one experiment involving prairie voles, a socially monogamous rodent species, individuals separated from their partners showed a measurable increase in anxiety-like behavior. When reintroduced to their partners, however, their stress indicators rapidly normalized. [■][3] The mechanisms behind this response are still being explored, but it is believed that close social bonds trigger the release of neurochemicals such as oxytocin, which in turn modulate stress pathways in the brain. [■][4] Understanding how social structures mitigate stress may not only reveal new insights into animal welfare but also inform the development of treatments for stress-related disorders in humans.

59. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Similar evolutionary changes occurred with other instruments, such as the lute gradually transforming into the modern guitar."

Excerpt:

During the Renaissance period, musical instrument craftsmanship flourished across Europe, with many regions developing distinctive styles and techniques. The lute, widely popular in the 15th and 16th centuries, was originally a string instrument with a rounded back and multiple courses of strings. [■][1] Skilled artisans enhanced the lute’s construction, improving sound quality and playability, which contributed to its widespread appeal among musicians and composers. [■][2] Around this time, instrument makers began to experiment with design modifications, leading to the gradual transformation of some traditional instruments. [■][3] This era also saw the rise of printed music, which encouraged the dissemination of new compositions and performance practices. [■][4]

60. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Collectively, these cultural exchanges laid the groundwork for the Renaissance, fostering new ideas in art, science, and philosophy."

Excerpt:

The Silk Road was more than just a network for trading goods; it was a vital conduit for cultural interaction between East and West. For centuries, merchants, travelers, and scholars journeyed across vast deserts and mountain ranges, carrying not only silk and spices but also religions, languages, and technologies. [■][1] This continuous exchange helped spread Buddhism from India to China, introduced paper-making techniques to the Islamic world, and brought Greek philosophical texts to the attention of medieval scholars. [■][2] The mingling of ideas stimulated intellectual curiosity and artistic innovation across diverse societies, creating a fertile environment for cross-cultural collaboration. [■][3] These interactions transformed local customs and knowledge systems, contributing to the emergence of new artistic styles and scientific methods in regions connected by the trade routes. [■][4]

61. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This raises important questions about how dietary patterns have influenced human physiology over millennia."

Excerpt:

Recent studies of ancient human diets have revealed surprising insights into how our ancestors adapted to various environmental conditions. [■][1] Contrary to the once-popular belief that early humans primarily hunted large game, archaeological evidence suggests a more diverse diet that included plants, tubers, nuts, and small animals. In particular, dental analysis from pre-agricultural societies shows significant wear patterns consistent with chewing tough, fibrous plant material. [■][2] This challenges the modern notion that meat consumption was the dominant feature of human evolution. Moreover, isotope analysis of bones from different continents indicates substantial regional variation in nutrient intake, shaped by climate, geography, and cultural traditions. [■][3] For instance, communities in coastal regions consumed more seafood, while inland groups relied heavily on starchy roots and wild grains. These dietary differences likely led to distinct metabolic adaptations in populations over time, such as varying lactose tolerance or insulin sensitivity. [■][4] Today, researchers continue to examine how these ancient adaptations may explain modern disparities in health outcomes, including susceptibility to obesity, diabetes, and cardiovascular disease in different populations.

62. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Like Robert Boyle, another prominent chemist of the time, he conducted experiments that focused on the role of air and air particles in combustion and respiration."

Excerpt:

In the field of chemistry, the understanding of the word “air” has undergone radical change. Air for John Mayow, a seventeenth-century chemist, was essentially a receptacle for airborne particles, and through them manifested a variety of chemical properties. [■][1] But although Mayow and a few other chemists did detect specific chemical properties in what we call gases (including our carbon dioxide), most chemists left them unaccounted for until the beginning of the eighteenth century. [■][2] As chemists became aware that the atmosphere itself (and not just particles within it) had a role to play in combustion, respiration, and other reactions, they did not attribute this to the chemical properties of air but rather to substances that air could absorb and release according to circumstances. [■][3] Thus, air provided a physical environment in which some reactions took place.

[■][4] In the early 1700s, the air was widely seen as just such an environment, and “air” and "the air" were one and the same thing. Chemists were not in the habit of regarding airs or gases as having different chemical properties. There was simply air. One obvious reason for this was practical. Chemists could examine solids and liquids, exposing them to a variety of tests and seeing how they contributed to assorted reactions. Chemists had, however, no comparable way of examining air; and they came to view chemistry as the sum total of the reactions of solids and liquids, excluding gases. Chemists stressed chemical qualities over physical properties like weight and let physicists deal with air. Chemists generally did not examine air, and they did not try to weigh it. That does not mean that chemists did not weigh substances. They did a lot of weighing, and pharmacists and metallurgists did more. But weighing gases was outside their brief. In the Encyclopedia of Diderot and d’Alembert, published between 1751 and 1775, readers were told that “the incoercibility of gases will remove them from our researches for a long time to come.”

63. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Some ancient instruments underwent development; for instance, the shawm became the oboe."

Excerpt:
In the 1600s, northern Italy emerged as the global center for violin manufacturing. In the town of Cremona, families such as the Amati, Guarneri, and Stradivari pioneered craftsmanship techniques that made their violins highly prized by Europe’s elite courts. [■][1]. These methods, passed down through generations, were kept so secret that modern violinmakers have never managed to replicate them fully. [■][2]. In other areas around 1650, older instruments were refined and standardized. [■][3]. Also during this time, music-making among amateurs became common, while professional performances flourished as new virtuosos inspired written guides on technique. [■][4].

64. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These developments demonstrate how innovations and environmental pressures have jointly shaped the complexity of human societies."

Excerpt:

Throughout history, societies have undergone significant changes driven by both technological advancements and environmental factors. The invention of agriculture allowed for stable food supplies, leading to larger populations and the formation of cities. [■][1] Innovations such as irrigation and plowing increased productivity but also required new forms of social organization to manage resources effectively. [■][2] Meanwhile, environmental challenges like droughts, floods, and soil depletion tested the resilience of these early civilizations, forcing adaptations and sometimes causing decline. [■][3] Social structures evolved to address these issues, with governing bodies and trade networks emerging to coordinate efforts and distribute resources. [■][4]

65. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Such adaptation involved changes in hunting and food gathering that make it possible to identify distinct Mesolithic periods and cultures in some regions."

Excerpt:
The European Mesolithic (approximately 8000 B.C. to 2700 B.C.) reflects a cultural continuity from the end of the Ice Age. [■][1] This continuity, however, was made possible through ongoing adaptations to the environmental transformations that occurred after the last glacial period, which ended around 12,500 years ago. [■][2] Three major phases of the Mesolithic period have been identified in Scandinavia. [■][3] The Maglemose phase (7500–5700 B.C.) featured seasonal use of rivers and lakes, alongside land-based hunting and gathering. [■][4] The following Kongemose phase (5700–4600 B.C.) centered on coastal areas along the Baltic Sea, where communities relied on both sea and land resources. Many of these sites are larger than their Maglemose predecessors. The Ertebølle phase (4600–3200 B.C.) marked the peak of Mesolithic life in southern Scandinavia.

66. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Cities would not only provide job opportunities but also profoundly affect social patterns, standards of living, political movements, and ideologies."

Excerpt:
Much of the increased production was consumed by Great Britain’s burgeoning population. At the same time, people were moving to the city, partly because of the enclosure movement; that is, the fencing of common fields and pastures in order to provide more compact, efficient privately held agricultural parcels that would produce more goods and greater profits. In the sixteenth century enclosures were usually used for creating sheep pastures, but by the eighteenth century new farming techniques made it advantageous for large landowners to seek enclosures in order to improve agricultural production. Between 1714 and 1820 over 6 million acres of English land were enclosed. [■][1] As a result, many small, independent farmers were forced to sell out simply because they could not compete. [■][2] Non-landholding peasants and cottage workers, who worked for wages and grazed cows or pigs on the village common, were also hurt when the common was no longer available. [■][3] It was such people who began to flock to the cities seeking employment and who found work in the factories that would transform the nation and, the world. [■][4]

67. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Such individual efforts had substantial, concrete effects on society."

Excerpt:
The greater reliability of food supplies was a factor in the decline of urban death rates. [■][1] Even more important were the gains in urban sanitation, as well as measures such as inspection of housing. [■][2] Reformers, including enlightened doctors, began to study the causes of high death rates and to urge remediation. Even before the discovery of germs, beliefs that disease spread by “miasmas” (noxious forms of bad air) prompted attention to sewers and open garbage; Edwin Chadwick led an exemplary urban crusade for underground sewers in England in the 1830s. [■][3] Gradually, public health provisions began to cut into customary urban mortality rates. [■][4] By 1900, in some parts of Western Europe life expectancy in the cities began to surpass that of the rural areas. Industrial societies had figured out ways to combine large and growing cities with population growth, a development that would soon spread to other parts of the world.

68. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Infrared radiation can be perceived directly by a few animals that have specialized sense organs that respond to this type of radiation."

Excerpt:
[■][1] It is thought that the facial pits or pit organs on the head of some snakes are specialized infrared (heat) receptors. [■][2] When a rattlesnake strikes, the direction of the strike seems to be guided by the infrared radiation from its prey. [■][3] A rattlesnake strikes only at warm-blooded prey, and when the prey is dead and at room temperature, the snake will not strike. [■][4] However, a blindfolded snake strikes correctly at a dead rat that is pulled across the cage, provided the rat is warmer than the surroundings. Blindfolded, the snake cannot be guided by vision; nor is it guided by the sense of smell, for it will strike correctly even at a moving, cloth-wrapped electric bulb. The pit organs are evidently involved in sensing the location of warm objects. All snakes that have pit organs feed preferentially on warm-blooded prey, and this further supports the view that these organs are infrared sensors. In the rattlesnake the pit organs are located, one on each side, between the nostril and the eye; they are connected to many nerves, and this in itself suggests a sensory role for the organ.

69. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These visual records offer clues not only about attire, but also about social status, occupation, and even beliefs."

Excerpt:

Painted portraits from ancient civilizations serve as more than just artistic representations—they are valuable historical documents. [■][1]. For example, Roman-Egyptian funerary portraits from the Fayum region depict individuals in stunning detail, often including jewelry, hairstyles, and clothing. [■][2]. Such portraits help scholars reconstruct aspects of daily life that textual sources rarely mention. [■][3]. Because many of these individuals were buried with their portraits, researchers can also match painted images to skeletal remains, allowing for comparisons between artistic style and biological reality. [■][4]. Advances in imaging and pigment analysis have revealed even more about the materials used and the cultural influences reflected in the artwork.

70. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This versatility makes it a preferred choice when designing components for aircraft and spacecraft."

Excerpt:

There are several reasons titanium is favored as a material in advanced engineering applications. [■][1]. One of its most notable qualities is its high strength-to-weight ratio, which allows structures to be both strong and lightweight. [■][2]. Titanium is also highly resistant to corrosion, even in extreme environments such as seawater or strong acids. [■][3]. Additionally, it can withstand high temperatures without losing its structural integrity, making it suitable for demanding thermal conditions. [■][4]. For these reasons, titanium continues to play a vital role in modern industries where performance and reliability are critical.

71. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Several of these have been named after their discoverers."

Excerpt:
Knowledge of Earth's deep interior is derived from the study of the waves produced by earthquakes, called seismic waves. Among the various kinds of seismic waves are primary waves (P-waves) and secondary waves (S-waves). [■][1] Primary and secondary waves pass deep within Earth and therefore are the most instructive. [■][2] Study of abrupt changes in the characteristics of seismic waves at different depths provides the basis for a threefold division of Earth into a central core; a thick, overlying mantle, and a thin, enveloping crust.[■][3] Sudden changes in seismic wave velocities and angles of transmission are termed discontinuities.[■][4]

72. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This is not the only example of a large-scale translocation that had positive results."

Excerpt:
An example of apparent translocation success involves the threatened Seychelles warbler. This species was once confined to Cousin Island, one of the Seychelles islands, and reduced to 26 individuals. Careful habitat management increased this number to over 300 birds, but the single population remained vulnerable to local catastrophic events. [■][1] The decision was taken to translocate individuals to two nearby islands to reduce this risk. [■][2] The translocations took place in 1988 and 1990, and both have resulted in healthy breeding populations. [■][3] A successful translocation exercise also appears to have been achieved with red howler monkeys in French Guiana. [■][4] A howler population was translocated from a site due to be flooded for hydroelectric power generation. The release site was an area where local hunting had reduced the density of the resident howler population. Released troops of monkeys were kept under visual observation and followed by radio tracking of 16 females. Although the troops appeared to undergo initial problems, causing them to split up, all the tracked females settled into normal behavioral patterns.

73. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This distinction allows scientists to trace the evolutionary pathways that led to complex multicellular life."

Excerpt:

Multicellularity is a hallmark of complex organisms, but its origins remain one of the most intriguing questions in evolutionary biology. [■][1]. Among single-celled organisms, certain species form colonies that behave cooperatively, but not all such groupings qualify as truly multicellular. [■][2]. True multicellularity involves permanent cooperation, with cells specializing in different functions and often being unable to survive on their own. [■][3]. In contrast, colonies are typically composed of identical cells that can separate and live independently under the right conditions. [■][4]. Understanding how some simple colonies transitioned into integrated multicellular organisms helps reveal key moments in life’s history.

74. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Such observations underscore the importance of carefully controlled conditions when interpreting behavioral data from laboratory studies."

Excerpt:

Animal cognition research has made remarkable strides in recent decades, but it remains fraught with interpretative challenges. [■][1] One major difficulty lies in distinguishing between learned behavior and genuine understanding. For example, when a parrot appears to "count" objects or respond to questions, is it demonstrating numerical competence or simply responding to subtle cues given by the experimenter? [■][2] This phenomenon, known as the “Clever Hans effect,” refers to cases where animals seem to exhibit advanced cognitive skills but are actually reacting to unintentional signals from humans. [■][3] In one well-known case, a horse named Hans was believed to solve arithmetic problems, but later tests revealed he was picking up on barely perceptible shifts in posture and facial expressions from his trainer. This effect has since been observed in studies involving dogs, dolphins, and even primates. [■][4] As a result, researchers have developed more stringent protocols, such as double-blind setups, to ensure animals are not simply mirroring human expectations.

75. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This is one reason researchers often combine multiple techniques to gain a more complete picture of ancient materials."

Excerpt:

Analyzing ancient artifacts requires a range of scientific methods, each with its own strengths and limitations. [■][1]. Techniques such as X-ray fluorescence (XRF) allow scientists to determine the elemental composition of materials without damaging the artifact. [■][2]. However, XRF cannot distinguish between different chemical compounds, which limits its ability to provide precise molecular information. [■][3]. Raman spectroscopy, on the other hand, offers insights into molecular structures but can be sensitive to interference from surface contamination or background fluorescence. [■][4]. Other methods, such as infrared spectroscopy or mass spectrometry, may provide further data, but even these are not universally applicable. [■][5]. Despite these challenges, the growing availability of portable instruments and collaborative approaches has enhanced our ability to study archaeological materials more thoroughly than ever before.

76. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"In many contexts—grasslands and most other types of forest, for example—that inference would be correct."

Excerpt:
On viewing the lush plant growth of a tropical rain forest, most people would conclude that the soil beneath it is rich in nutrients. [■][1] However, although rain forest soils are highly variable, they have in common the fact that abundant rainfall washes mineral nutrients out of them and into streams. [■][2] This process is known as leaching. [■][3] Because of rain leaching, most tropical rain forest soils have low to very low mineral nutrient content, in dramatic contrast to mineral-rich grassland soils. [■][4] Tropical forest soils also often contain particular types of clays that, unlike the mineral-binding clays of temperate forest soils, do not bind mineral ions well. Aluminum is the dominant cation (positively charged ion) present in tropical soils; but plants do not require this element, and it is moderately toxic to a wide range of plants. Aluminum also reduces the availability of phosphorus, an element in high demand by plants.

77. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Other developments addressed the problems of dry and sandy areas unsuitable for growing China’s native crops."

Excerpt:
This technological advance took many forms: one was the continual introduction from the south of earlier-ripening varieties of rice, which made possible double-cropping (the production of two harvests per year from one field). [■][1] New crops such as corn (maize) and sweet potatoes as well as peanuts and tobacco were introduced from the Americas. [■][2] Corn, for instance, can be grown on the dry soil and marginal hill land of North China, where it is used for food, fuel, and fodder and provides something like one-seventh of the food energy available in the area. [■][3] The sweet potato, growing in sandy soil and providing more food energy per unit of land than other crops, became the main food of the poor in much of the South China rice area. [■][4]

78. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Other plants, however, possess additional defenses against freezing temperatures."

Excerpt:
Most of the needle-leaved conifers of the northern and alpine forests, such as pines, spruces, and firs, do not lose their leaves during the winter. How do such evergreen plants escape intracellular freezing (freezing within cells) and tissue destruction when temperatures may drop to -40°C or colder? In these plants, the onset of cool temperatures causes physiological changes that allow plant tissue to either avoid freezing or restrict freezing to extracellular areas (those outside of cells). For plants to avoid freezing, they must chemically alter their liquids into a form that is analogous to antifreeze in automobiles. The liquids in these plants can be cooled far below 0°C and will not freeze. This process is called supercooling and is achieved by the metabolic synthesis of sugars and other molecules which, when in solution in the plant's tissue, lower the temperature for ice formation to far below 0°C.[■][1]. Supercooling seems to be the prevalent mechanism of frost resistance in herbs.[■][2]. For woody plants, supercooling is augmented by declines of cellular water content, greater cellular accommodation to deformation, and processes that allow water to accumulate and freeze in extracellular spaces.[■][3]. The loss of water from the cells to extracellular areas increases the solute content (the quantity of dissolved substances) of the remaining cell water, making it more resistant to freezing.[■][4]. The cell walls can accommodate the deformations caused by water freezing on the exterior of the cell. For northern and alpine evergreens such as pines and spruces, both supercooling and extracellular ice formation play a part in allowing the plants to withstand extremely cold temperatures. One interesting facet of these physiological adaptations to freezing is that most of these plants will still be damaged by cold temperatures if they do not have a period of cooling in which to adjust to the onset of winter. This process of physiological preparation for the onset of winter cold is called frost hardening.

79. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Their prompt realization of this connection helped to strengthen their position as the new official ruling class."

Excerpt:
[■][1]Later generations of Chinese scholars of the Song Dynasty (A.D.960-1279) quickly recognized the link between the bronzes and jades and political power.[■][2] In their search for political legitimacy, they collected and studied ancient artifacts, pursuits that in themselves reinforced the high status of jade and bronze in society.[■][3] From the idea that political power resided in ancient objects, including calligraphy and painting, grew the first art Collections.[■][4]

80. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"To answer the question “Could life exist on other planets?” we must first look at the necessary preconditions for life."

Excerpt:
[■][1] The creation of life requires a set of chemical elements for making the components of cells. [■][2] Life on Earth uses about 25 of the 92 naturally occurring chemical elements, although just 4 of these elements—oxygen, carbon, hydrogen, and nitrogen—make up about 96 percent of the mass of living organisms. [■][3] Thus, a first requirement for life might be the presence of most or all of the elements used by life. [■][4]

81. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Despite extensive research, the reasons for their sudden disappearance remain a topic of ongoing debate among historians."

Excerpt:

The Maya civilization flourished in Mesoamerica for over a thousand years, known for its sophisticated writing system, impressive architecture, and advanced knowledge of astronomy. [■][1]. At its peak, the civilization spanned modern-day Mexico, Guatemala, Belize, and parts of Honduras and El Salvador. [■][2]. The Classic Period of Maya history saw the construction of grand cities such as Tikal and Palenque, featuring massive temples and elaborate ball courts. [■][3]. However, by the end of the 9th century, many southern cities were mysteriously abandoned, leading to what scholars refer to as the “Maya collapse.” [■][4]. Archaeologists have proposed various explanations for this decline, including environmental degradation, warfare, drought, and social upheaval, but no single cause has been universally accepted.

82. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This perk is especially useful in fields like logistics and urban planning, where tiny inefficiencies can scale into significant delays or resource loss."

Excerpt:

Computer simulations have become a critical tool for researchers and professionals aiming to understand and predict the behavior of complex systems. [■][1] Whether applied to biological ecosystems or transportation networks, simulations offer a controlled environment where variables can be adjusted without real-world risk. [■][2] One significant advantage is the ability to run repeated trials quickly, allowing users to identify patterns, anomalies, or optimal configurations across a wide range of scenarios. [■][3] Another key benefit is that simulations make it possible to visualize system-wide impacts caused by small local changes—something that’s often impossible to gauge in physical settings due to time, cost, or safety concerns. [■][4] While simulations are not a perfect substitute for real-world testing, their efficiency and adaptability have made them indispensable across many disciplines, from environmental science to manufacturing.

83. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"It produced constant disputes and conflicts between neighboring states."

Excerpt:
As the volume of long-distance trade increased dramatically, so competition over resources intensified.[■][1] Each state raised an army to defend its water rights, trade routes, and city walls.[■][2] The onerous tasks of defense and military organization passed to despotic kings supposedly appointed by the gods.[■][3] Such Sumerian city-states as Erech, Kish, and Ur had periods of political strength and prosperity when they dominated their neighbors.[■][4] Then, just as swiftly, the tide of their fortunes would change and they would sink into obscurity.

84. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Such findings complicate earlier models that attributed language acquisition solely to genetic predisposition."

Excerpt:

The study of how children acquire language has fascinated linguists and psychologists for decades. [■][1] Traditional theories often emphasized innate biological mechanisms, suggesting that humans are born with a universal grammar that guides language learning. However, extensive cross-cultural research has revealed significant variability in the way languages are learned and used. [■][2] For example, some societies use extensive verbal interaction with infants, while others rely more heavily on nonverbal communication during early childhood. Observations also show that environmental factors such as social interaction, exposure to multiple languages, and educational practices can dramatically influence the speed and nature of language acquisition. [■][3] These findings indicate that while genetics provide a foundation, the environment plays an equally crucial role in shaping linguistic competence. [■][4] Researchers are now exploring how this interplay between biology and environment affects not only language development but also cognitive functions more broadly.

85. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"For example, before European impact, the western island of Bougainville in the Solomons had several thousand plant species, while Easter Island had only 30."

Excerpt:
Life arrived on most other islands by accident or by drift. Some plants arrived by air transport, seeds carried in the digestive tracts of birds account for nearly 40 percent of Hawaii’s early plants. The first invaders were either creatures that could float well enough, in air or water, to cross stretches of ocean, or those whose seeds could survive a voyage in some bird's gut. [■][1] At times of lower sea level, land bridges linked, or nearly linked, many islands in the far western Pacific, so some species colonized these islands without being notably good floaters or stowaways. [■][2] In the eastern Pacific (Easter Island, for example) only the best floaters and travelers arrived and survived. [■][3] Consequently, the western islands have far more species and far greater biodiversity than do the eastern islands of Polynesia. [■][4] Mammals found it hard to get anywhere in the island Pacific; only bats and rats successfully colonized east of New Guinea. Almost all species derive from Asia; the early Pacific was an Asian lake, with only a tiny proportion of species from the Americas. As a rule of thumb, the further from Indonesia, the more impoverished the plant and animal life and, in consequence, the less stable and resilient in the face of disturbance. This attenuation is strong for land species, less strong for marine species, and nonexistent for oceanic birds, although fairly strong for land birds.

86. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Flying was thought to require more energy than cold-blooded reptiles were capable of generating."

Excerpt:
Pterosaurs also possessed some obvious adaptations for powered flight. They had large sternums (breastbones) for attaching powerful flight muscles, well-developed shoulder bones to carry the body's weight in flight, and air-filled bones to lighten the skeleton. [■][1] Some even had a furcula (a fused breastbone also found in birds), perhaps to flex like a spring and help raise the wings during the upstroke. [■][2] How competent were they at flying? The original batlike reconstructions, along with their classification as reptiles, suggested to many earlier biologists that pterosaurs were only gliders. [■][3] Biologists now, however, generally agree that pterosaurs were capable of powered, flapping flight. [■][4] Indeed, the shoulder joint is clearly specialized for the down-and-forward, up-and-back movement of normal flapping.

87. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The complex interplay between linguistic relativity and spatial orientation becomes especially evident in communities that use geocentric, rather than egocentric, references."

Excerpt:

Language does more than communicate ideas—it can shape how speakers perceive and interact with the world around them. [■][1] One striking example is found in the way people from different cultures talk about spatial relationships. In English and most European languages, spatial orientation is typically described using egocentric coordinates such as "left" and "right," which are based on the individual's point of view. [■][2] However, in some Indigenous Australian languages, such as Guugu Yimithirr, people rely on geocentric coordinates like "north," "south," "east," and "west," regardless of their current position. This means that even when indoors or in unfamiliar terrain, speakers of these languages must maintain constant awareness of cardinal directions to describe simple movements or object locations. [■][3] Research has shown that this linguistic habit fosters superior navigational skills and spatial memory compared to speakers of egocentric languages. In one experiment, children who spoke geocentric languages were better able to reorient themselves in a rotated room than their egocentric-speaking counterparts. [■][4] Such findings suggest that language not only reflects cultural priorities but may also train cognitive systems in specific ways, with implications for how humans develop and maintain spatial awareness across diverse environments.

88. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These ranged from Alexandria, Egypt, to Algeria, to the Crimean peninsula in the Black Sea, to Sardinia, Ibiza, Crete, and Cyprus."

Excerpt:
Venice carefully built its reputation as a reliable supplier, and so contracts with the merchant state were desirable. Venice was able to dictate terms for these contracts. In 1250, when Venice agreed to supply Mantua and Ferrara with salt, the contract stipulated that these cities would not buy salt from anyone else. [■][1] This became the model for Venetian salt contracts. [■][2] As Venice became the salt supplier to more and more countries, it needed more and more salt producers from which to buy. Merchants financed by the salt administration went farther into the Mediterranean, buying salt from many distant sources. [■][3] Wherever they went, they tried to dominate the supply, control the saltworks, and even acquire them if they could. [■][4]

89. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Ultimately, these interconnected elements have driven the continuous evolution and adaptation of human societies over millennia."

Excerpt:

Human history is characterized by the interaction of multiple forces, including environmental conditions, technological innovations, and social organization. Early humans adapted to diverse climates by developing tools and strategies suited to local resources. [■][1] The rise of agriculture transformed nomadic groups into settled communities, fostering population growth and complex social hierarchies. [■][2] Technological breakthroughs, such as metallurgy and written language, further enabled cultural transmission and economic expansion. Societies often faced challenges like resource scarcity, conflict, and environmental degradation, which prompted innovations or migrations. [■][3] These factors were rarely isolated; instead, they influenced each other in complex and dynamic ways, shaping the path of civilizations around the world. [■][4]

90. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"Scholars remain divided on the origins and purposes of these mysterious structures."

Excerpt:

Stone circles are found in various parts of the world and date back thousands of years. [■][1]. These formations often consist of large standing stones arranged in circular patterns, sometimes accompanied by smaller stones or burial mounds. [■][2]. Some researchers believe the circles functioned as astronomical calendars, marking solstices and equinoxes with precise alignments. [■][3]. Others argue that they were primarily ceremonial sites for religious gatherings or social events. [■][4]. Recent excavations have uncovered artifacts that support both interpretations, suggesting the structures may have served multiple roles over time.

91. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"These advantages made it appear to be the perfect solution, and farmers began to use it in large quantities."

Excerpt:
Melander offered his ideas in 1914, but no one paid much attention to him; they were too busy discovering even more powerful pesticides. [■][1]. In 1939 the Swiss chemist Paul Müller found that a compound of chlorine and hydrocarbons called DDT could kill insects more effectively than any previous pesticide had. [■][2]. DDT was cheap and easy to make, it could kill many species of insects, and it was stable enough to be stored for years. [■][3]. It could be used in small doses, and it didn’t seem to pose any health risks to humans. [■][4]. Between 1941 and 1976, 4.5 million tons of DDT were produced. DDT was so powerful and cheap that farmers gave up old-fashioned ways of controlling pests, such as draining standing water or breeding resistant strains of crops.

92. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The typeface that followed was italic, with a slanted appearance in the style of handwriting and a name that was recognizably Italian."

Excerpt:
Although there was no competition between the technologies, there was rivalry between nations. The Italians made energetic and successful efforts to catch up with Germany. Their most successful scriptorium quickly imported two leading German printers to set up presses in their book-producing shop. [■][1] German printers had the disadvantage of working with the complex typeface that the Italians sneeringly referred to as “Gothic” and that later became known as black letter. [■][2] Outside Germany, readers found this typeface disagreeable. [■][3] The Italians, on the other hand, had a clear typeface known as roman that became the type of the future. [■][4]

93. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"One possible nonhuman cause—weather cycles—is not consistent with what scientists know about the timing of the extinctions."

Excerpt:
[■][1] Although the climate changed at the end of the Pleistocene, warming trends had happened before. [■][2] A period of massive extinction of large mammals like that seen about 11,000 years ago had not occurred during the previous 400,000 years, despite these changes. [■][3] The only apparently significant difference in the Americas 11,000 years ago was the presence of human hunters of these large mammals. [■][4] Was this coincidence or cause-and-effect?

94. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"One such study specifically monitored the activity of individuals navigating through complex indoor environments without auditory cues."

Excerpt:

For decades, scientists assumed that blind individuals navigated primarily through a combination of touch and hearing. [■][1] Echoes, cane taps, and ambient sounds all contribute to a spatial map that helps blind individuals move through their surroundings. However, more recent research has challenged the idea that hearing alone can account for the high level of navigation accuracy often demonstrated by blind participants in experimental settings. [■][2] Neuroimaging studies have shown that the brains of blind individuals repurpose the visual cortex to process non-visual information in spatial ways. This neural plasticity allows for the enhancement of senses like touch and hearing, but it also suggests the development of spatial reasoning mechanisms that do not rely entirely on those senses. [■][3] In controlled experiments where auditory input was limited or removed altogether, blind participants were still able to make accurate judgments about obstacles and distances, implying the involvement of alternate pathways of spatial processing. [■][4] These findings have prompted a reevaluation of how sensory information is integrated and used for navigation, suggesting that the brain’s adaptability is far more complex than previously believed.

95. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"This is so because no evidence of domestication such as enlargement of grain size or thinning of seed coats has survived in these regions."

Excerpt:
[■][1] Between 9,000 and 4,000 years ago, most of Mexico was inhabited mainly by hunter-foragers who lived in small bands that moved with the seasons to exploit cactus fruits, deer herds, nuts, and the hundreds of other plant and animal species in their range, depending on the season. [■][2] Since these bands were small in size and never stayed in one place for a sufficient period of time to have much long-term effect on the plant and animal populations on which they subsisted, the hunter-foragers' overall impact on their environment was low. [■][3] A few groups along the margins of the lake in the Valley of Mexico may have been sedentary villagers, as were some groups along the coasts, and their role in the domestication of plants and animals and the eventual spread of agriculture is unclear. [■][4] Some researchers suggest, however, that by about 4,000 years ago, maize cob size had become large enough that people over large areas of the Mexican highlands could subsist mainly on maize.

96. Directions:
Look at the four squares [■] that indicate where the following sentence could be added to the passage.

Sentence to Insert:
"The social status of the Mayans largely determined where they lived."