高中英语情态动词单选题

As nobody here knows what is wrong with the machine, we          send for an engineer to handle the problem．

A．should

B．must

C．can

D．would

We should spend as much time as we _______ over our lessons.

A．go

B．can to go

C．can go

D．can going

Not having work out the problem,          leave the office．

A．so he was not allowed to	B．and he didn’t want to
C．the teacher couldn’t make him	D．he couldn’t free himself to