21.—— We have to stop talking here outside. Listen， _______!

　　—— Hurry up， or we‘ll be late.

　　A. There goes the bell B. There does the bell go C. There the bell goes D. Goes the bell there

　　22.The factory _______ we‘ll visit next week is not far from here.

　　A. where B. to which C. which D. in which

　　23.—Why didn‘t you buy a new car?

　　—I would have bought one if I _______ enough money.

　　A. had B. have had C. would have D. had had

　　24.There was so much noise that the speaker couldn‘t make himself ________.

　　A. hear B. heard C. hearing D. to hear

　　25.This is an important problem _______ too few social scientists have researched.

　　A. which B. that C. into that D. into which

　　26.They ________ extensive and possibly dangerous actual flight training.

　　A. undertake B. undergo C. underplay D. underuse

　　27.They will get the preparation done early in May.

　　A. 他們五月初就能讓別人準備完工作

　　B. 他們五月初就能準備好工作

　　C. 他們早在五月份就能把準備工作做完

　　D. 他們五月初就能把準備工作做完

　　28.Weather _______， we‘ll go out for a walk.

　　A. permitted B. permitting C. permits D. for permitting

　　29.I don‘t think the charge for overhauling the equipment is excessive in _______ to its size.

　　A. correspondence B. equation C. proportion D. dimension

　　30.It is difficult to understand this kind of _______ calculation.

　　A. intricate B. varied C. indispensable D. equable