—Why does the lake smell terrible?
—Because large quantities of water _____.
| A．have polluted. | B．is being polluted. |
| C．has been polluted. | D．have been polluted. |
The guidelines are _______ in the second paragraph.
| A．heard out | B．set out | C．lived out | D．pointed out |
Perce Blackborow and his companions stayed on Elephant Island for six months before rescue came, so they ________ a lot of difficulties.
| A．must go through | B．may go through |
| C．must have gone through | D．could have gone through |
Written in a hurry, __________________ .
| A．they found many mistakes in the report | B．he made lots of mistakes in the report |
| C．there are a lot of mistakes in the report | D．the report is full of mistakes |
Is it the country ________ you studied ________ you are going to visit next week?
| A．in which; which | B．where; that | C．that; that | D．where; where |
Why do you always drive to work _______ you could easily take the bus?
| A．because | B．though | C．once | D．when |