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标题: 新PREP破解上的一道题，求助NN [打印本页]

作者: dandanapple 时间: 2010-4-30 06:55 标题: 新PREP破解上的一道题，求助NN

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

作者: xiangzhengj 时间: 2010-4-30 22:20

大天体撞击星球或者月亮，物质就会被喷射出来，从而产生一个大洞和质量不足。质量不足

反映为重力场的不规则：导致大洞的重力低于周围的地区，因此，人们推测月亮上的环形山show

负的重力不规则，即重力比周围小因此，人们推测月亮上的环形山show负的重力不规则，即重力

比周围小，然而，后来，月球变冷，不再有弹性...因此，今天重力的补偿不可能再出现了。
with the most significant negative gravity，而文章讨论的moon反常的地方恰恰是在早期出

现，如果出现典型负重力场那么就应该是不冷没弹性的，所以e是不对的
e是两个矛盾的条件说到一起了~

作者: dandanapple 时间: 2010-5-4 06:47

compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin-----早期是no gravity anomaly,然后后面moon less elastic----现在的significant anomaly,所以E就应该是错的了，恩，终于懂了，谢谢楼上的啊~~

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