21. To get a better view of the stage, ____.

　　A. our seats had to be changed B. our seats were changed

　　C. we had to change our seats D. our seats were changed by us

　　22. After synthetic____, engineers had a better choice of material.

　　A. created B. has created

　　C. has been created D. had been created

　　23. I think much attention ____your pronunciation.

　　A. must be paid to B. ought to be paid to

　　C. must pay to D. should be paid to

　　24. Since 1970, millions of enthusiasts ____Vitamin C, which they believe can remedy the common cold.

　　A. have taken B. have been taken

　　C. have been taking D. have been taking

　　25. I don't remember ____the chance to try this method.

　　A. having been given B. to have been given

　　C. having given D. to have given

　　26. We could ask someone to do the work privately without it____.

　　A. know B. be known

　　C. being known D. to be known

　　27. The construction of the laboratory ____by the end of next month.

　　A. must be completed B. must have been completed

　　C. will be completing D. will have been completing

　　28. They would tell how the African ____on a ship to an American port.

　　A. was brought B. could have been brought

　　C. had been brought D. was to be brought

　　29. He does not possess a bicycle, this one he uses ____to Peter.

　　A. is belonged to B. belonged

　　C. belongs D. is belonging

　　30. Negotiation ____again with Moscow tomorrow, a great event will be discussed then.

　　A. is to be opened B. is on the point of opening

　　C. is going to open D. opens

　　31. The reason for all the changes being made ____to us yet.

　　A. has not explained B. has not been explained

　　C. did not explained D. were not explained

　　32. Experiments in the photography of moving objects ____in both the United States and Europe well before 1900.

　　A. were conducting B. were conducted

　　C. had been conducted D. had conducted

　　33. When he turned the corner, he found himself ____by a man in black.

　　A. tailed B. been tailed

　　C. was tailed D. had been tailed

　　34. A candidate for the democratic presidential nomination ____at this moment.

　　A. is interviewing B. being interviewed

　　C. is being interviewed D. interviewing

　　35. As we approached the work site, the workers were seen ____the new house.

　　A. building B. build

　　C. built D. to build

　　36. As we know, all the regulations in school ____.

　　A. must keep to B. must be kept

　　C. must keep D. must be kept up

　　37. The composition ____any more.

　　A. need not to be corrected B. doesn't need to be corrected

　　C. doesn't need be corrected D. need not correct

　　38. The bank is reported in the local newspaper ____in broad daylight yesterday

　　A. to be robbed B. to have keen robbed

　　C. robbed D. having been robbed

　　39. Hurry up, or the tickets ___out by the time we get there.

　　A. will have sold B. will sell

　　C. have sold D. will have been sold

　　40. He cleaned the glasses carefully for fear that it ____.

　　A. was damaged B. should be damaged

　　C. damaged D. would be damaged