Question

【题目】Scientists have advanced many theories about why human beings cry tears, none of ______ has been proved.

A. whom B. which C. what D. that

Answer 1

【答案】 B

【解析】句意：关于人类为什么哭的时候会流泪，科学家已经提出了很多理论，没有一个被证明了。此句为定语从句，先行词是theories，指物，定语从句用＂代词+介词+关系代词which＂引导。故选B。