Question

I don’t know _________

1. A.
   what   to   do   it
2. B.
   how   to   do
3. C.
   what   to   do
4. D.
   to   do   what

Answer 1

C
考查非谓语动词. 疑问词加不定式作用相当于一个宾语从句，句意:我不知道做什么.选项AD结构有误,选项Bhow不能做宾语,故选C