---I am going to Japan.
--- How long_____ you_____ there ?
| A．are; stayed | B．are; staying | C．have; stayed | D．did; stay |
We _____ on this project for four hours. Let’s have a rest.
| A．are working | B．have been working |
| C．worked | D．had worked |
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 |