Food safety is one of the problems now all over the world.
| A．discussed | B．to be discussed |
| C．being discussed | D．having been discussed |
30．It's a good habit to have your car brakes ______ before a long journey．
| A．to check | B．checked | C．checking | D．Check |
29．—The cleaning must have taken you quite a long time yesterday．
—Right．The rooms ______ for two months．
| A．haven't been cleaned | B．didn't clean |
| C．hadn't been cleaned | D．hadn't cleaned |
28．Kids are often told to remain ______ they are and wait for their parents if they get lost．
| A．what | B．where | C．how | D．Who |
27．—What did you ______ while in college?
—English, politics and economics．
| A．take up | B．think up | C．bring up | D．make up |
26．I called Nancy many times but couldn't get through．Someone ______ on the phone all the time!
| A．has been talking | B．was talking |
| C．has talked | D．Talked |