135. 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.

A. which, causing plant and animal extinctions, marks

B. which caused the plant and animal extinctions marking

C. and causing plant and animal extinctions that mark

D. an event that caused plant and animal extinctions, and it marks

E. an event that caused the plant and animal extinctions that mark

A: which 指代不清

B: 同上

C: and causing 和前面没有对称的对象

D: it指代不清

E: correct

为什么it指代不清,it不是就是指event吗?

为什么it指代不清,it不是就是指event吗?