31.By the time we _____the airport, the plane_____.
| A．arrived at; had taken off | B．had got to; took off |
| C．got to; had taken away | D．arrived at ; had taken away |
This is the very knife _____ I used to cut apples yesterday.
| A．that | B．by which | C．which | D．with which |
---- Is it high time that we _____ on the school building?
---- Yes, it _____.
| A．do some repairs; is | B．do some repair; is |
| C．did some repairs; is | D．did some repair; was |
The cost of sales makes up a large part of the prices that _____.
| A．are paid for all products |
| B．all products are paid |
| C．for which all products are paid |
| D．for all products paid |
The captain stood by the window, _____ he could see the top of the tower.
| A．where | B．from which |
| C．from where | D．which |
That was the only gate _____ we could rush out and save those _____ were in great danger.
| A．that; which | B．which; who |
| C．through which; who | D．at which; who |