Question

Before the problem can be solved，it must be obvious ________ the problem itself is.(2011·湖南，31)

A．what

B．that

C．which

D．why

Answer 1

A

句意：在解决问题之前必须弄清楚问题本身是什么。what引导主语从句，并在主语从句中充当表语。注：句中的it是形式主语。