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Here is the detailed explanation for this question-
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Some scientists believe that 65 million years ago an asteroid struck what is now the Yucatan Peninsula, thereby causing extinction of the dinosaurs. These scientists have established that such a strike could have hurled enough debris into the atmosphere to block sunlight and cool the atmosphere. Without adequate sunlight, food sources for herbivorous dinosaurs would have disappeared, and no dinosaurs could have survived a prolonged period of low temperatures. These same scientists, however, have also established that most debris launched by the asteroid would have settled to the ground within six months, too soon for the plants to disappear or the dinosaurs to freeze.
Which one of the following, if true, most helps to resolve the apparent discrepancy between the scientists’ beliefs and the scientists’ results, as described above?
(A) Loss of the herbivorous dinosaurs would have deprived the carnivorous dinosaurs of their food source.
(B) Dinosaurs inhabited most landmasses on the planet but were not especially abundant in the area of the asteroid strike.
(C) A cloud of debris capable of diminishing sunlight by 20 percent would have cooled the earth’s surface by 7 to 10 degrees Celsius.
(D) The asteroid was at least 9.6 km in diameter, large enough for many dinosaurs to be killed by the strike itself and by subsequent tidal waves.
(E) Dinosaurs were susceptible to fatal respiratory problems cause by contamination of the air by asteroid debris.
Mind-map: Asteroid struck -> debris hurled -> sunlight blocked -> destruction of food for herbivorous dinosaurs + cold weather led to extinction -> but, debris would have settled too soon for plants to vanish and dinosaurs to freeze.
Missing link: Between belief that debris blocked sunlight and led to extinction and the result that debris would have settled too soon for plants to vanish and dinosaurs to freeze.
Expectation from the correct answer choice: To resolve discrepancy by suggesting why dinosaurs got extinct though plants did not vanish and dinosaurs did not freeze.
Choice A: This answer choice, in suggesting that the carnivorous dinosaurs were deprived of their food, assumes the extinction of herbivorous dinosaurs; however, the question clearly mentions that the scientists also established that the debris settled before the plants were destroyed and so there is no basis for concluding that the herbivorous dinosaurs became extinct; as it does not explain the reason for extinction and the apparent discrepancy, this answer choice is not correct.
Choice B: This answer choice focuses on areas inhabited by the dinosaurs and not on the reason for extinction or the discrepancy; hence, it is an irrelevant choice. By suggesting that dinosaurs were not especially abundant in the area of asteroid, this answer choice, if anything, is only complicating the discrepancy rather than resolving it.
Choice C: This answer choice focuses on some background information, which does not address the reason for extinction or the discrepancy in the argument; besides, the question clearly mentions that the lack of sunlight or the cold temperature was not enough to lead to the death of the dinosaurs; hence, this answer choice is extremely weak and fails to resolve the discrepancy; it is, therefore, not the correct answer choice.
Choice D: This answer choice mentions that “many” dinosaurs were killed by the strike and the subsequent tidal waves but that is not likely to lead to their extinction; as the answer choice does not explain the reason for extinction and address the discrepancy, it is not a fine answer choice.
Choice E: By suggesting an additional effect caused by the strike, this answer choice explains why the dinosaurs would have become extinct even though the plants were not destroyed and the temperature did not lead to the dinosaurs freezing to death; the debris was hurled into the atmosphere, inhaled by the dinosaurs, and affected their respiratory tract; this proved to be fatal and led to their extinction; as this answer choice addresses the discrepancy in the argument by explaining the reason for extinction, it is a fine answer choice.
Hence, E is the best answer choice. To understand the concept of "Characteristics of an Explanation Statement on GMAT Critical Reasoning", you may want to watch the following video (~2 minutes):
All the best!
Experts' Global Team