They did not stop fighting_____ there was no enemy left.
| A．until | B．after | C．when | D．since |
The computer system broke _____ suddenly while he was searching for information on the Internet．
| A．down | B．out | C．up | D．in |
He was so busy that _____ I could say hello to him he had rushed out of the room．
| A．when | B．before | C．since | D．until |
If we work hard with a strong will, we _____ overcome any difficulty, however great it is．
| A．must | B．need | C．should | D．can |
—Did Betty go shopping with you yesterday?
—Even if she _____ a lot of studying, she would have preferred staying home to going shopping．
| A．didn’t have | B．shouldn’t have |
| C．hadn’t had | D．hasn’t had |
With masses of homework _____, I can hardly spare time to practice playing the piano．
| A．done | B．to do | C．doing | D．being done |