求助一语法题：prep 126题

allygmat7

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
正确答案是E，可是我不明白的是，mark为什么用谓语动词的复数形式呢