21. While other scientists are keeping__ __eye on changes in the H5N1 bird flu strain, the scientists in England are working on vaccines, in case it becomes highly infectious in __ __humans.
  A. a , /       B. an, /        C. the, an          D. an, the
22. ____ him so far, she felt a little worried.
     A．Having not hear from          B．Not having heard from
     C．Not hearing from              D．Have not heard from
23. A man who will ______ his life for his country is a true man.

A. dedicate     B. promote       C. sacrifice         D. devote

24. Most of the students in our school adore ______ to the cinema.

A. to go          B. go           C. going            D. to going

25. After much _______, the shop owner agreed to cut down the price by 15%.

A. debating       B. talking       C. discussing         D. bargaining

26. The officer demanded that such things ________ from happening again.

A. prevented     B. prevent       C. be prevented      D. were prevented

27. Children must _______ road safety before they are allowed to ride a bike on the road.

A. instruct in      B. instruct      C. be instructed in    D. be instructed

28. Mary was so touched by Tom’s generosity that for a moment she was _______ for words.

A. in loss         B. in a loss        C. at loss           D. at a loss

29. Most of the world’s rice is grown in the tropical _______.

A. section        B. location        C. district          D. zone