I don’t understand ____ believe him.

问题描述:

I don’t understand ____ believe him.
A.why don’t you B.why you not C.why you don’t D.why not you
为什么选C不选A?

因为这不是问句.问句才可以把don't等之类放在前面.上面的句子改为问句:Why don't you believe him?