______________

A．To account for the comet's composition of ice and dust.

B．To show the effect of Jupiter's gravity on the comet's orbit.

C．To explain why the comet is not visible from Earth very often.

D．To argue that the comet's orbit should not be considered periodic.

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参考答案

答案解析

【预测】选项均为动词不定式短语，结合其中重复出现的comet’s orbit以及comet’s composition，Jupiter和Earth可知，本题可能考查某种目的，可能与彗星和其他天体的关系有关。
【解析】C。录音中教授提到，因为哈雷彗星大多数时间处于木星的运行轨道之外……所以我们每75年才有几个月的时间能够观察到它，由此可推知，教授通过强调这个时间解释了为什么我们在地球上不能经常看到哈雷彗星的原因，故答案为C。

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