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When a large body strikes a planet or moon, material is ejected, thereby creating a hole in the planet and a local deficit of mass. This deficit shows up as a gravity anomaly: the removal of material that has been ejected to make the hole results in an area in slightly lower gravity than surrounding areas. One would therefore expect that all of the large multi-ring impact basins on the surface of earth's moon would show such negative gravity anomalies, since they are, essentially, large holes in lunar surface. Yet data collected in 1994 by the Clemenstine spacecraft show that many of these Clementine basins have no anomalously low gravity and some even have anomalously high gravity. Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin. Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such gravitational compensation probably would not occur: the outer layer of moon is too cold and stiff.
The Passage suggests that if the scientists mentioned in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably
A) were not formed early in the Moon's history
B) were not formed by the massive ejection of crustal debris
C) are closely surrounded by other impact basins with anomalously low gravity
D) were created by the impact of multiple large impactors
E) were formed when the moon was relatively elastic
这道题我选了E,知道A对的原因，但是为什么E不对呢，请NN给出自己的解题思路，你是怎么考虑这道题的，不是单纯解释答案，谢谢啦 |
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京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2010-2-4 00:39:27
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