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：

A. That

(答案→)B. What

C. Whether

D. Where

解析：主语从句连接词的选用。分析该句中主语部分的结构可知，空格中应填一个作主语的连接词。在所给的四个连接词中，只有what能充当主语，故选B项。