22.The windows of our house _____once a week.

  A. must clean         B. have cleaned      C. is cleaned           D. are cleaned

21. This English song _____ often _____ by the children.

  A. is, singing          B. is, sung              C. will, sing            D. was, sung

20. Man-made satellites ______into space by many countries.

  A. was sent up       B. is sent up

  C. have been sent up                              D. has been sent up

19. Chang'an Road is ______of people.

  A. filled                  B. fill                      C. full                     D. fulled

18. They ______day and night.

  A. are made work B. are made to work

  C. made to be worked                           D. are making to work

17. We can't enter the room because its door______ .

  A. locked               B. locks                  C. is locked            D. is locking

16. When water______ , it will be changed into vapor(蒸汽).

  A. is heated            B. heating               C. has heated         D. heats

15. The war______ in 1941.

  A. broke out           B. had been broken out

  C. was broken out D. had broken out

14. I ______the way to the railway station by a policeman.

  A. was shown        B. showed              C. have shown       D. was showing

13. We can't use the bridge now, because it______ .

  A. has been repaired                              B. is repairing         C. is repaired       D. is being repaired