31．Every solid object______reflect a sound，varying according to the size and nature of the object．
| A．must | B．shall | C．will | D．Should |
I’m afraid none of us can __________ the machine that has been imported from abroad.Which of the following is wrong?
| A．work | B．run | C．turn | D．operate |
In Britain,sales of cigarettes have been reduced __________ 30% in the past ten years.
| A．for | B．to | C．from | D．by |
Whenever you are to walk on the ice,__________ that it is solid and safe enough.
| A．examine | B．check | C．try | D．make |
It is a __________ that you missed such a wonderful concert.
| A．shame | B．pity | C．regret | D．mistake |
Because of the snow,many parts of the countryside are only _________ by helicopter.
| A．available | B．appropriate | C．accessible | D．achievable |