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

问题补充：

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

A. whether

B. that

C. what

D. when

答案：

A. whether

B. that

(答案→)C. what

D. 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。