The old couple have been married for 40 years and never once ___________ with each other．
| A．they had quarreled | B．they have quarreled |
| C．have they quarreled | D．had they quarreled |
What will people die of in 100 years? If you think that is a simple question, you ______ attention to the revolution taking place in biotechnology.
| A．have not been paying | B．had not been paying |
| C．were not paying | D．will not be paying |
The government has taken some measures to solve the shortage of electricity, but it may be some time _________ the situation improves.
| A．since | B．when | C．before | D．unless |
Mandela, having devoted all his life to the freedom of South African Blacks, is a real fighter for us to_________.
| A．live up to | B．come up to | C．make up to | D．look up to |
You cannot imagine what great trouble I took ______ your house.
| A．to find | B．finding | C．found | D．having found |
Jordan kept his illness from his opponents before the final game ________ they might know about it.
| A．now that | B．on condition that | C．for fear that | D．in order that |