Many students didn’t realize the importance of study _______ they left school.

I think ______ people drive， ______ air pollution there will be.—That’s true. I hope the air will be fresher soon.

David has been in high spirits these days— ______ He should win the first prize in thecomposition test

_______ both sides accept the agreement will the two countries live in peace

We can never forget the days _______ the three astronauts in spaceship worked together and the days ________ we spent together [ ]