what to do和how to do it 的区别
这两个短语都是特殊疑问词加不定式构成的,相当于宾语从句.
what to do是完整的（what是do的宾语）,表示做什么,故不定式后不可再加宾语,
如
I don't know what to do.
(= I don't know what I can do .)
how to do是不完整的（how提问方式）,必须加上do的宾语,表示如何做、、、
如
I don't know how to dothis thing.
(= I don't know how I can do this thing.)
一般情况do后必须加上宾语.