Scientists say it may be five years ______ it is possible to test this medicine on human patients．
| A．since | B．until | C．before | D．when |
________ there is no restriction on foreign entries at the film festival ，those that win are in minority.
A. unless B. When C Where D while
________ seems to be a strong competition in China for senior high students to enter college or university.
| A．It | B．This | C．That | D．There |
It is no use _________ to persuade him ________ smoking because he has been addicted to it since he was
young.
| A．trying, to quit | B．to try, to quit | C．to try, quit | D．trying, quit |
I would have come earlier, but I ________ that you were waiting for me.
| A．hadn’t known | B．didn’t know | C．would have known | D．haven’t know |
five hours to the meeting, David learnt that it had been postponed.
| A．Having driven | B．Driven | C．Being driven | D．To be driven |