HOW是对方式状语提问;WHAT是对表示事物的主语,宾语,表语等提问。 I don't know what to do. (用what是因为不定式to do后缺宾语),I don't know how to do it. ( 用how是因为不定式to do后有宾语it,我们也可以用when,where, why 等表示状语的疑问词)
how与when/where/why一样是副词,当句子不缺少主语和宾语时,用how意思是“怎么样” what是代词,当句子缺少主语或宾语时用what,意思是“什么” 例如:I don't know what to do. I don't know how to do it. do需要跟宾语,缺少宾语,用what,而不缺少宾语用how 希望对你有帮助