what must he do?

what must he do? what "must"i/we/you/he/she/they do and what "must not'' i/we what must i do? 怎么用语法解释这句话“you must do as he says”.如果是“you must do what he s he will have to stay in hospital. that's what he must do .这是 请教what must they do When one is learning a foreign language,what must he do. What must one do if he wants to learn another language well? WHAT MUST THEY DO?TH EY MUST DO THEIR HOMEWORK what he should do What could he do? what people must to do the ocean