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题库解析   >   其他题型   >   RC1-4篇
    本题由hyman1提供
135次学习
RC1-4篇

This passage was excerpted from material published in 1996.

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 the material that has been ejected to make the hole results in an area of 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 the lunar surface. Yet data collected in 1994 by the Clementine spacecraft show that many of these lunar 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 low gravity anomaly in the resulting basin. Later, however, as the 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 the Moon is too cold and stiff.

According to the passage, the gravitational compensation referred to in

the highlighted text is caused by which of the following?

    A.A deficit of mass resulting from the creation of a hole in the lunar surface

    B.The presence of material from the impactor in the debris created by its impact

    C.The gradual cooling and stiffening of the Moon's outer layer

    D.The ejection of massive amounts of debris from the Moon's crust

    E.The rapid upwelling of material from the lunar mantle


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答案:
E

By caused by

意思是由什么引起,很明显引力补偿是由于表面质量缺失引起的,E选项是对这个名词的解释,求解释

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