The public transport system in Beijing is very good now, so there _____be any difficulty in traveling around the city.
| A．couldn’t | B．mustn’t | C．needn’t | D．shouldn’t |
________ in Tibet for ten years, he has been accustomed to the life and the climate there.
| A．He has worked | B．Having worked |
| C．He has been working | D．Working |
30. Look! What a mess the room is! In my opinion, it needs ______.
| A．cleaning up | B．being cleaned up | C．to clean up | D．clean up |
--- Don’t waste any paper, because our forests ____ every day.
----Sorry, I didn’t know that.
| A．decreased | B．had decreased | C．have decreased | D．are decreasing |
. The child, who 
has a gift for sports, might make a first-class tennis player if given chances to develop her ______.
| A．courage | B．habit | C．potential | D．sense |
---Did Jack come back early last night?
---Yes, it was at eight o’clock_____ he arrived home.
| A．before | B．when | C．that | D．until |