请问Prep上一题

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

E，an event是做什么成分啊？

which 通常出現在修辭考題時,多半都是錯誤的選項,這是因為which通常造成指代不清的現象,以本題為例,which可指an asteroid bigger than Mount Everest slammed into North America或North america,產生岐義.

加上an event可清楚指明是an asteroid bigger than Mount Everest slammed into North America這件事造成動植物滅絕.a的marks明顯錯誤,b which語意不清,c slammed跟causing不對稱,d 的it應該是指plant and animal extinctions,不是指an event.

难道是做整个前面这句（即这一事件）的同位语？有这种同位语吗？