31．We were swimming in the lake _______ suddenly the storm started. (Beijing 2004 spring)

　　 A. when　　　　　 B. while　　　　　 C. until　　 　 D. before

30. _____ modeling business is by no means easy to get into, the good model will always be in demand.　　　　 A. While B. Since 　C. As　　　 　　　D. I　 　　(2004 Zhejiang)

29. Several weeks had gone by ______I realized the painting was missing.(NMET2004-4)

A. as　 　　　　　　B. before　 　　　　C. since　 　　　D. when

27. Roses need special care _____ they can live through winter. 　　　(NMET2004-1) 　　 A. because 　　　　B. so that 　　　　C. even if 　　　D. as 28. _____you call me to say you' re not coming, I'll see you at the theatre.(NMET2004-2) 　　 A. Though 　　　　　B. Whether 　　　　C. Until 　　　　D. Unless

26. You can eat food free in my restaurant ____ you like.　　　　　　 (Chongqinog 2004)

　 　A. whenever　　 　　B. wherever　　　 　C. whatever　　 　D. however

25. Don’t be afraid of asking for help ____ it is needed.　　　　　　 (NMET2003)

A. unless　　　 　　B. since　　　　 　C. although　　　 D. when

24. -Was his father very strict with him when he was at school?　 -Yes. He had never praised him_____ he became one of the top students in his grade.　　　　　 (2003Spring)

A. after 　　　　　B. unless 　　　　　C. until 　　　　D. when

23. _______ I know the money is safe, I shall not worry about it.　　 (2003Beijing)

A. Even though　 　　B. Unless 　　　　　C. As long as　　 D. While

22. He made a mistake, but then he corrected the situation _______ it got worse.

A. until　　　　　 　B. when　　 　　　　C. before 　　　　D. as　　　 (2003Beijing)

21. Mr. Hall understands that ___ math has always been easy for him, it is not easy for the students.　　　　　　　　　　　　　　 (2003Anhui)

A. unless 　　　　　B. since　　　　 　C. although 　　　D. when