Thanks to scientific research, we now have a good understanding of an earthquake is and why it happens.
A. how
B. which
C. whether
D. what
网友回答
A. how
B. which
C. whether
(答案→)D. what
解析:经分析,of是介词,后接宾语从句,而is是系动词,后接表语,故应选D。本句含义,多亏了科学研究,现在我们对什么是地震以及为什么发生地震有了很好的了解。