Answer: Option D
:
D
This question asks you to identify a prediction that can be derived from both the conventional theories about meteor streams and the new computer-derived model. You must base your answer on information that is suggested by, but not expressly stated in, the passage. According to the passage, the conventional theories hypothesized that meteor streams should broaden with time, and the computer simulation confirmed this hypothesis. The passage also suggests that the time it takes for the Earth to cross a meteor stream (and, by implication, the duration of the resulting meteor shower) is directly related to the breadth of the stream. From these pieces of information, which are supported by both the conventional theories and the new computer-derived theory, it can be inferred that on average the meteor showers caused by older (and therefore broader) meteor streams would be longer in duration than those caused by very young (and therefore narrower) meteor streams, as stated in D, the best answer. Choice A is incorrect because it contradicts the predictions of both the conventional theories (that the particles will be most dense at the center of the stream) and the computer model (that the stream will resemble a thick-walled, hollow pipe). Choice C is also incorrect because it is inconsistent with the conventional theories that suggested the distribution of dust in a meteor stream is denser at the center. And choice B is incorrect because the theories discussed in the passage do not suggest anything about the likelihood that the Earth’s orbit will cross that of any particular meteor stream.