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  3. The primary focus of the passage is on which of the following? Which of the following is an assumption underlying the last sent

The primary focus of the passage is on which of the following? Which of the following is an assumption underlying the last sent

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问题 The primary focus of the passage is on which of the following?
Which of the following is an assumption underlying the last sentence of the passage?
选项 A、In each of the years between 1970 and 1979, the Earth took exactly 19 hours to cross the Geminid meteor stream.
B、The comet associated with the Geminid meteor stream has totally disintegrated.
C、The Geminid meteor stream should continue to exist for at least 5,000 years.
D、The Geminid meteor stream has not broadended as rapidly as the conventiona ltheories would have predicted.
E、The computer-model Geminid meteor stream provides an accurate representation of the development of the actual Geminid stream.
答案E
解析 This question asks you to identify an assumption underlying the last sentence of the passage. In this sentence, the author of the passage draws a conclusion about the age of the Geminid stream. This conclusion is based on two pieces of information. The first is the length of time the Earth would take to cross the computer-model Geminid stream if the stream were 5,000 years old (lines 24-28). The second is the actual elapsed time between the two peaks of meteor activity predicted by the computer model (lines 36-40). In concluding from this information that the Geminid stream is actually only 3,000 years old, the author is assuming the accuracy of the computer model, as stated in E, the best answer. Choice A is incorrect because the passage says that the time the Earth takes to cross the stream would vary from year to year (lines 32-34) and that 19 hours was the average time, not the exact time, observed from 1970 to 1979 (lines 36-40). Choices B and C are incorrect because the passage does not suggest anything about the current state of the comet associated with the Geminid stream or about the expected longevity of the stream. Choices D is incorrect because the computer model is said to confirm the broadening predicted by the conventional theories; the fact that the model projected the positions of the particles in the stream over a 5,000-year period does not suggest that researchers expected the stream to be older (and therefore broader) than it turned out to be.
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