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题库 / Prep2007E2-SC-69
Sixty-five million years ago, according to some scientists, an asteroid bigger than Mount Everest slammed into North America, which, causing plant and animal extinctions, marks the end of the geologic era known as the Cretaceous Period.
which, causing plant and animal extinctions, marks
which caused the plant and animal extinctions marking
and causing plant and animal extinctions that mark
an event that caused plant and animal extinctions, and it marks
an event that caused the plant and animal extinctions that mark
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老师为什么是animal extinctions mark而不是这个事件marks
Ron对这个的解释是觉得D中用了现在式有些奇怪，毕竟是过去发生的。当然我们也被教导说现在式是用作真理，客观情况的。所以我也不知道该如何抉择。。。。
D中it指代的是asteroid，不应该是asteroid marks the end，小行星本身并不能标志一个时代的终结。
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