I don’t know .A. what to do it B. how to do C. what to do D. to do what

问题补充：

I don’t know .

A. what to do it

B. how to do

C. what to do

D. to do what

答案：

A. what to do it

B. how to do

(答案→)C. what to do

D. to do what

解析：what什么;how怎样;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. 结合语境可知选C.