30. He will come ____ you ask him.　　　

A. whether　　　 B. unless　　 C. if　　 D. while

29. Everything around us is ____ solid ..liquid ____ gas.

A. not .. .but...　 B. either.. .or... C. neither.. .nor... D. whether.. .or...

28.It is late; ____, I'm too tired to go out.　

A. besides　 B. except　 C. except for　 D. except that

27. We have produced 15% more cotton this year____ we did last year.

A. as　　　　　 　　　　 B. than　　 　　 C. like　　 D. white

26.____ the problem of method is solved, talking about the task is useless.

A. Until　　　　　　 B. Since　　　　　　　　 C. After　　　　　　 D. Unless

25. Where have you been ____ you left home?　　

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

24.____ you told me, I had heard nothing of what happened.　

A. Till　 B. Until　 C. After　 D. Since

23. He ran off____ I could stop him.　　　　

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

22. We should pay attention ____ to industry ____ to agriculture.

A. either, or　　 　 B. neither, nor　　 C. not, but　　　 　 D. both, and

21. My sister is expecting me,____ I must be off now.　 　

A. however　 B. or　 C. so　　 D. otherwise