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

C. what to do

D. to do what

答案：

A. what to do it

B. how to do it

(答案→)C. what to do

D. to do what

解析：考查疑问词+不定式。what to do中，what作do的宾语，A项it多余，排除A；D项的疑问词应该放前面，排除D。 how to do中缺少宾语，排除B。故选C。