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题库 / Prep2007E1-SC-136
It seems likely that a number of astronomical phenomena, such as the formation of planetary nebulas, may be caused by the interaction where two stars orbit each other at close range.
may be caused by the interaction where two stars orbit each other
may be caused by the interaction between two stars that each orbit the other
are because of the interaction between two stars that orbit each other
are caused by the interaction of two stars where each is orbiting the other
are caused by the interaction of two stars orbiting each other
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ing和从句是没有区别的，two stars that orbit each other=two stars orbiting each other，
名词和ing的区别在于ing侧重于过程，名词侧重于结果，ing的动作在句子中没有明确的结束时间点，名词则有明确的结束时间点，如：
(1) Exploring the cave is taking a long time.
(2) The exploration of the cave took three days.
句(1) 中我们完全看不到“探索山洞”这件事的终止点，只是知道已经花了很长的时间了，可能还将继续花很长的时间；句(2)中，主句部分已经用过去时表明“花费了3天”，由此可知，“探索山洞”这件事已经完结了，具备明确的时间终点。
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