No scientists can exactly figure out what _______

试题详情及答案解析

No scientists can exactly figure out what ________ happened ________ at that time, which caused the extinction of the dinosaurs.

A．on earth; on the earth

B．on the earth; on earth

C．on earth; on earth

D．on the earth; on the earth

答案：A

试题分析：考查短语辨析。句意：没有科学家能够弄清楚当时地球上到底发生了什么事情，这件事导致了恐龙的灭绝。on earth到底，究竟；on the earth在地球上，故选A。
考点：考查短语辨析