TOEFL Reading Practice Test #53

Explanation:
Paragraph 1 explains that transgenic plants often contain either a gene for herbicide resistance or an insect-resistant gene that produces the Bt toxin. The Bt toxin specifically makes the plant resistant to insects, not herbicides.

D. is correct; Bt-producing plants are engineered to resist insect damage.
A. is incorrect; resistance to herbicides is provided by a different gene, not the Bt gene.
B. is incorrect; although 68 percent of transgenic crops are grown in the U.S., the passage does not claim that Bt plants grow “best” there.
C. is incorrect; glyphosate is used with herbicide-resistant plants, not with Bt resistance.

Explanation:
Paragraph 2 states that proponents argue transgenic crops are environmentally friendly because they allow farmers to reduce the use of harmful chemicals. For example, Bt cotton reduces insecticide use by 21 percent, and glyphosate use replaces the need for more persistent herbicides.

B. is correct; the primary benefit highlighted is reduced use of chemicals that are more noxious.
A. is incorrect; the 21 percent figure refers specifically to reduction in insecticide use, not increased crop production.
C. is incorrect; glyphosate is still used to control weeds in herbicide-resistant crops.
D. is incorrect; the focus is on reducing the need for other herbicides, not on accessing more effective ones.

Explanation:
Paragraph 3 mentions that monarch caterpillars feed on milkweed near Bt cornfields and may consume Bt pollen. While lab studies show some can die from Bt pollen, field studies suggest Bt corn is unlikely to harm them. Monarch caterpillars are examples of nontarget organisms that could be affected by transgenic crops.

C. is correct; the passage classifies them as beneficial insects affected by Bt crops.
A. is incorrect; there is no suggestion that monarchs damage crops.
B. is incorrect; the passage notes that some caterpillars can die from Bt pollen, so they are not immune.
D. is incorrect; their reactions have been studied both in laboratories and in field tests.

Explanation:
Paragraph 4 discusses how herbicide-resistant genes can move from transgenic plants to weedy relatives. The passage explains that if the resistant gene is passed to offspring, it remains in the weed population over time.

A. is correct; "perpetuated" refers to the gene being continued in subsequent generations.
B. is incorrect; while reproduction occurs, the emphasis is on the gene being maintained in the population rather than just being reproduced.
C. is incorrect; "observed" does not capture the idea of persistence.
D. is incorrect; "spread" implies movement to new locations, not continued existence within a population.

Explanation:
Paragraph 4 explains that herbicide-resistant genes can be passed from crop plants to nearby weedy relatives through hybridization, potentially creating resistant weeds. The mention of mustard weed species illustrates a real example of a weed that can acquire the herbicide-resistant gene from canola.

A. is correct; it directly provides an example of a weed that could gain resistance through hybridization.
B. is incorrect; the point is not about creating transgenic plants in a laboratory.
C. is incorrect; the passage does not discuss competition as the main concern.
D. is incorrect; while proximity to weeds is mentioned, the focus of the example is the potential transfer of resistance, not the difficulty of maintaining distance.

Explanation:
Paragraph 5 discusses how continuous exposure to Bt toxin in transgenic plants can select for resistant insects, and how planting nontransgenic border rows can help maintain Bt susceptibility in the population. It also notes that conventional Bt pesticide use has not historically created resistant populations because exposure was not continuous.

A. is correct; the paragraph explains that historical Bt pesticide use did not lead to resistant populations, but it does not claim that Bt plants are therefore safe—this overgeneralizes.
B. is incorrect; the paragraph clearly indicates that widespread use of Bt plants will eventually lead to resistant insect populations.
C. is incorrect; the passage explains that Bt plants express the toxin continuously, leaving only resistant insects alive.
D. is incorrect; using nontransgenic border rows is described as a strategy to preserve Bt susceptibility in the population.

Explanation:
The highlighted sentence emphasizes that the main concern is that current transgenic crop plants encourage farmers to adopt less sustainable practices, specifically those that do not allow natural resources to regenerate over time.

1. Incorrect; this option discusses future transgenic plants, which is not mentioned in the highlighted sentence, so it changes the focus.
2. Incorrect; this reverses the meaning, suggesting farmers are moving toward sustainable practices, which contradicts the warning in the highlighted sentence.
3. Correct; it accurately paraphrases the highlighted sentence by stating that transgenic plants may replace sustainable practices and identifies this as their main concern.
4. Incorrect; while close, it is too vague and general. It fails to specify that the concern is the move away from sustainable agricultural practices, which is essential to the original sentence.

Explanation:
The passage says that transgenic crops “at least superficially, simplify farming,” meaning that on the surface they seem to make farming easier, but this does not capture the deeper implications for sustainability.

A. is incorrect; the word does not refer to experts’ opinions.
B. is incorrect; it does not relate to timing.
C. is incorrect; it is not about proper methods.
D. is correct; “superficially” means “without deeper analysis” or “only on the surface.”

Explanation:
The sentence fits best at [4] because it provides a specific explanation of why the scenario described in the preceding sentence—hybridization with weedy relatives—is uncommon in the United States. It clarifies that most crops in the U.S. do not have nearby weedy relatives because they originated elsewhere.

1. Incorrect; inserting the sentence here would disrupt the logical flow before explaining how the resistant gene moves into weed populations.
2. Incorrect; this spot continues the explanation of how hybridization affects weeds, so adding the sentence here interrupts the process.
3. Incorrect; the sentence does not belong here because the focus is on what happens if hybridization occurs, not why it is rare.
4. Correct; this placement follows naturally from the discussion of rarity and provides context before the example of canola and mustard weed.

Explanation:
The summary should focus on the most important points about the benefits and potential risks of transgenic plants.

A. Correct; this reflects the passage’s discussion that transgenic plants can reduce pesticide use and allow environmentally friendly herbicides.
B. Correct; this captures the concerns about herbicide resistance spreading to weeds and insects developing Bt resistance.
C. Correct; the passage emphasizes that transgenic crops may encourage less sustainable farming and can harm nontarget organisms.
D. Incorrect; while Bt may not affect all pests, the passage does not present this as a major point in the overall summary.
E. Incorrect; the passage does not state that glyphosate resistance will be lost over time; rather, it focuses on the spread of resistance and evolution of insects.
F. Incorrect; potential future improvements are not a main idea of the passage and do not belong in the summary.