1. Usually we don't realize how important nature is to us______ it is too late.
　　A. unless B. until C. if D. after
　　2．Go to bed early，______ you won't get up on time next morning.
　　A．then B．and C．but D．or
　　3．Tony is a clever boy，______ he usually fails in Chinese exams.
　　A．so B．but C．or D. because
　　4. Could you please give me your e-mail address ____ you go?
　　A. as soon as B. before C. after D. until
　　5. Don't get off the bus ____ it has stopped .
　　A. until B. if C. to D. for
　　6. He met many problems ____ he was going over his lessons .
　　A. before B. as soon as C. since D. while
　　7. We have been good friends ____ we joined the same ping-pong team.
　　A. after B. before C. since D. until
　　8. My brother is going to look for another job______the company offers him more money．
　　A. after B.when C unless D．besides
　　9. I didn't know he came back ____ I met him in the street.
　　A. since B. when C. until D. after
　　10. -Look! Here comes our school bus.
　　-No hurry. Don't get on it ______it has stopped.
　　A. until B. after C. since D. when
　　11. When someone is ill, he ____ she should try to smile at life.
　　A. and B. but C. or D. so
　　12. Come ____ see my family.
　　A. and B. or C. but D.until
　　13. - How long have you known the doctor ?
　　- ____ he helped me three years ago.
　　A. When B. Before C. Because D. Since
　　14. Study hard, ____ you'll fall behind the others.
　　A. and B. but C. or D. though
　　15．-Be careful， ____ you will make mistakes in your exams．
　　-I know that，Mum．One can never be too careful．
　　A．and B．or C．nor D．but
　　16．I arrived at the airport____ the plane had taken off．
　　A.after B．while C．when D．beflore
　　17.Uncle Wang gave all his savings to the Hope School____ he himself was not rich.
　　A.because B.as if C.though D.or
　　18. The dress fits me well,____ I don't want to buy it because it's too expensive.
　　A. so B. and C. or D. but
　　19. English is interesting, _____ I didn't like it at first.
　　A. and B. so C. but D. or
　　20. -Would you like to come to dinner tonight?
　　-I will ________ I'm not too busy.
　　A. and B. if C. so D. but
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