Something must be done to stop cutting down trees. ________ all the trees are cut down, the valuable soil will be washed away by the heavy rain.
| A．Whether | B．Unless |
| C．Once | D．Until |
. --So hard __________ in the past few months that he has made great progress in English.
--I can see that, only a few mistakes he made in this exam.
| A．he worked | B．did he work |
| C．he has worked | D．has he worked |
--How often do you visit your grandparents in the village?
--I feel ashamed. __________.
| A．Very often | B．By accident |
| C．Every now and then | D．All of a sudden |
--Who has broken the window in my room?
--Who else _________ it but your naughty son!
| A．could do | B．could have done |
| C．should have done | D．must have done |
. The concert by Lang Lang was so well _________ that all the tickets had been _________ on the first three days last month.
| A．received; sold out | B．recognized; sold out |
| C．admitted; selling out | D．taken; selling out |
They _________ on the program for almost one week before I joined them, and now we are still working on it as no good results have come out so far.
| A．have worked | B．had worked |
| C．have been working | D．had been working |