—Mr. Black, may I leave now?—Well, if your work ________, you can go home.
It is difficult for us to learn a lesson in life _______ we've actually had that lesson.
One fifth of the work _______ by computer last year.
This is the very thing ______ belongs _____.
She kept on _______ until midnight though he was tired.
The program is _______ interesting _______ I want to see it again.