Knowing , as a matter of fact, one shouldn’t know is a terrible thing．A. whetherB. thatC.

Knowing , as a matter of fact, one shouldn’t know is a terrible thing．
A. whether
B. that
C. what
D. when

A. whetherB. that(答案→)C. whatD. when解析：考查宾语从句，what为连接词作one shouldn’t know 的宾语，as a matter of fact,为插入语。句意：事实上一个人知道了不该知道的事情是非常可怕的。

这个答案应该是对的