must doing还是must to do?

must doing还是must to do? 是must to do还是must doing 还是must do? 是must be to do还是must be doing Attentions must be paid to do sth还是doing sth must not 后面加do doing 还是to do? 是must doing sth 还是to do sth? must do sth 还是 must to do sth We must keep_______exercise to keep heathly为什么填doing computers must be of great use to doing scientific research must 的用法是must sb do 还是must sb to do must When____the work,you must be careful.A do B are doing C to do D doing something must be done to pretect our enviroment.must后面为什么接done.而不能接doing请详解哦 He___his homework now.I know he has a lot of homework___.A must be doing/to do B must be doing/doing C can be doing/to do D can be doing/doing He will have to stay in hospital.That’s what he____a has done b must do c must be doing d must have done为什么C不对呢 must be do与must be doing 区别 something must do,something must not do must 加to must的否定?must的否定是need't还是don't have to?