This is not an economical way to get more water; ________, it is very expensive.
| A．in return | B．on the other hand | C．in a word | D．on the contrary |
It has been announced that candidates _____ remain in their seats until all the papers have been collected.
| A．can | B．will | C．may | D．shall |
Parents must take good care of their children, _____ they?
| A．mustn’t | B．don’t | C．needn’t | D．aren’t |
He must be in the reading-room, _____ he?
| A．mustn’t | B．doesn’t | C．needn’t | D．isn’t |
It was 4:25 a.m. _____ the ambulance arrived to take the body of Miss Lee.
| A．when | B．until | C．that | D．since |
It was years _____ I had visited my hometown in Dalian, Liaoning Province.
| A．after | B．that | C．since | D．when |