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.
(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
ANS:E
詳解說D選項是run-on sentence, 但我看不懂為甚麼run-on
可以幫忙解答一下嗎~~~感謝~