-----when has the country been open to international trade?
-----1978, I suppose.
| A．Since | B．In | C．From | D．After |
Though it was in the midnight, ________ there were a lot of people in the street.
| A．and | B．but | C．yet | D．however |
The ground isn't wet. It ________ have rained last night.
| A．mustn’t | B．shouldn’t | C．wouldn’t | D．can’t |
We tried to find a table for seven, but they were all _______.
| A．run out | B．taken up | C．used up | D．picked up |
In winter, it is dangerous to go to school with snow ______the ground.
| A．cover | B．to cover | C．covering | D．covered |
_______ late you are, we will wait for you to come to have dinner.
| A．Whenever | B．Whatever | C．However | D．Wherever |