Although this ______ sound like a simple task, great care is needed．
| A．must | B．may | C．should | D．shall |
Experiments of the kind ____ in both the U.S. and Europe well before the Second World Wall.
| A．have conducted | B．have been conducted |
| C．had conducted | D．had been conducted |
By the time Jane gets home, her aunt ____ for London to attend a meeting.
| A．will leave | B．will have left |
| C．leaves | D．left |
His sister left home in 1998, and ______ since.
| A．had not been heard of | B．has not been heard of |
| C．had not heard of | D．has not heard of |
The water ____ cool when I jumped into the pool for morning exercise.
| A．felt | B．is felt |
| C．was felt | D．feels |
The water supply has been cut off temporarily because the workers ____ one of the main pipes.
| A．are repairing | B．have repaired |
| C．repaired | D．had repaired |