he referred to in his article was unknown to the general reader. A. ThatB. WhatC. Whether

问题补充：

he referred to in his article was unknown to the general reader.

A. That

B. What

C. Whether

D. Where

答案：

(答案→)A. That

B. What

C. Whether

D. Where

解析：主要测试主语从句。句子 he referred to in his article在复合句中充当主语，同时该句子中缺少介词to的宾语，双重作用。答案一目了然。