You shouldn’t have the machines ______ all the while. You ought to have them ______ now and then.
The writer and professor, whom I often refer to at the meetings, ____ famous for those works.
She spent as much time as she could _____ over her lessons.
How about the rest of us _____ a meeting after dinner?
The blackboard was wiped _____ .
The students are _____ to hand in the exercises before class.