Before a problem can be solved it must be obvious the problem itself is. A. whatB. thatC.

问题补充：

Before a problem can be solved, it must be obvious the problem itself is.

A. what

B. that

C. which

D. why

答案：

(答案→)A. what

B. that

C. which

D. why

解析：考查主语从句：句意：在问题解决之前，问题本身是什么必须明确。it在句中做形式主语，真正的主语是what the problem itself is ，what在主语从句中做表语，选A。