24. They find it useful__________ (learn) English.

23.My friend can't decide which pair of trousers____________ (choose). So she asked me to go shopping with her.

22. All that must ________ (do).

21. A pen is used for__________ (write).

20. Jiefang trucks____________ (make) in Changchun.

19. He'll telephone us as soon as he _________ (arrive) there.

18. ----______ you ever_______ (be) to Beijing?　 ----Yes. I________ (go) there last week.

17. The students _____________ (do) their homework.　 __________ (not make) any noise!

16. Her mother____________ (cook) at this time yesterday.

15. It _________(rain) heavily when I got home.