题目选项分析

Sixty-five million years ago, according to some scientists, an asteroid bigger than Mount Everest slammed into North America, an event that caused the plant and animal extinctions that mark the end of the geologic era known as the Cretaceous Period.

Sixty-five million years ago, according to some scientists, an asteroid bigger than Mount Everest slammed into North America, an event that caused plant and animal extinctions, which marks the end of the geologic era known as the Cretaceous Period.