I don't know____I can do for you.A.who B.that C.what D.if为什么不选D呀,

I don't know____I can do for you.A.who B.that C.what D.if为什么不选D呀,
I don't know____I can do for you.A.who B.that C.what D.if为什么不选D呀,

I don't know____I can do for you.A.who B.that C.what D.if为什么不选D呀,
选 C what,引导宾语从句,what是指代从句中的宾语的.
如果你选D的话,从句就没有宾语了.如果从句说明了do什么for you,就应该选D.比如I don't know if I can do it for you.

C what 引导宾语从句，在从句中作 宾语。

在后面的宾语从句中，do缺宾语。if不可以做宾语，而what可以，并且符合句意。

貌似是初中英语吧，其实俺英语也挫，不过C就读的顺口