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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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ABC都很好排除，剩下DE。
D. an event that caused plant and animal extinctions, and it marks 这个it 我犹豫了很久，感觉像是an event；但回过头看其实it也可以指代 an asteroid；这就会造成指代不清的问题；
（遇到犹豫项一定要带回去看三次····提醒自己）
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