He doesn’t know.A. to do whatB. to do howC. what to doD. how to do

问题补充：

He doesn’t know.

A. to do what

B. to do how

C. what to do

D. how to do

答案：

A. to do what

B. to do how

(答案→)C. what to do

D. how to do

解析：句意：他不知道做什么。Know后面接的是宾补从句，疑问词后面用不定式，what to do做什么；故选C。