It was a serious mistake, ______ caused by carelessness.
| A．which I think was | B．which I think it was |
| C．I think which was | D．that I think it was |
Without gravity, we _____ walk on the ground as freely as we do now.
| A．couldn’t | B．mustn’t | C．shan’t | D．needn’t |
Zhang Heng, one of _____ best-known Chinese astronomers, showed a strong interest in _____ astronomy as a child.
| A．the; the | B．the; 不填 | C．不填; the | D．不填; 不填 |
— Could I have another cup of coffee, Daddy?
—_____ It will be hard for you to go to sleep tonight if you do.
| A．Better not. | B．Why not? | C．What for? | D．As you wish. |
With a report _____ about the accident, the policeman has to find some witnesses for help.
| A．write | B．writing | C．written | D．to write |
-The terrible accident might not have happened had the driver been more careful.
--But he _____.
| A．wasn’t | B．didn’t | C．hadn’t | D．doesn’t |