He had to go to the library.(改为一般疑问句)
Did he have to go to the library?
I have had to stay there for a week.(就＂for a week"提问)
How long have you had to stay there?
I have to go to the station early.(改为否定句)
I don't have to go to the station early.
He must finish his homework.(就"finish his homework"提问)
What must he do?