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
Last month, the Japanese government expressed their thanks for the aid they ______ from China.
A. receive B. had received C. have received D. are receiving
If you _____ smoke, please go outside because this is a non-smoking office.
A. must B. should C. can D. may
––Who would you rather _____ your graduation ceremony tomorrow, your parents or friends?
––All of them.
A. will have attended B. have attended C. attended D. to attend
In that school, English is compulsory for all students, but French and Russia are ____ .
A. special B. optional C. regional D. original
––Why didn’t you come to the party?
––I had meant _____, but something unexpected happened.
A. so B. that C. not D. to
