Only when you have finished your homework ______ go home.
| A．can you | B．would you | C．you will | D．you can |
If _____ carefully, the experiment will be successful.
| A．do | B．does | C．done | D．doing |
He is a man of few words, and seldom speaks until _____ to.
| A．spoken | B．speaking | C．speak | D．be spoken |
They kept trying _____ they must have known it was hopeless.
| A．if | B．because | C．when | D．where |
There are five pairs, but I'm at a loss which _____ to buy.
| A．to be chosen | B．to choose from | C．to choose | D．for choosing |
He was not an actor, who often appeared on stage, _____ a writer, writing stories.
| A．but | B．and | C．then | D．so |