(1) what 引导主语从句

例：What surprised me is that everybody seemed to be very indifferent to her.

    让我吃惊的是每个人似乎对她都很冷淡. [ indifferent adj.不关心的;冷漠的]

(2) what 引导宾语从句

例：We can learn what we do not know. 我们能学会我们不懂的东西。

(3) what 引导表语从句

例：That is what I want.   那正是我所要的。

(4) what 引导同位语从句

例：I have no idea what they are talking about. 我不知道他们正在谈论什么.