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10. We ______ open the lion’s cage. It is contrary to zoo regulations.
A. must
B. mustn’t
C. needn’t
D. should

11. When swimming in the pool, children ______ be accompanied by their parents.
A. can
B. could
C. don’t have to
D. have to

12. If you want to maintain a good relationship, you ______ behave impolitely like that.
A. ought to not
B. ought not to
C. mustn’t
D. don’t have

13. This drink isn’t beneficial for health. You ______ drink it too much.
A. should
B. ought to not
C. shouldn’t
D. mustn’t

14. This warning sign says that you ______ step on the grass.
A. shouldn’t
B. mustn’t
C. don’t have to
D. ought not to

15. I think you ______ do exercise regularly in order to keep in shape.
A. must
B. should
C. ought to
D. Both B and C are correct

16. My motorbike broke down yesterday, so I ______ catch a taxi to school.
A. have to
B. had better
C. had to
D. must

17. You look exhausted. You ______ take a rest instead of working overtime.
A. should
B. ought
C. must
D. has better

18. Those audiences ______ show their tickets before entering the concert hall.
A. have to
B. must
C. ought to
D. don’t have to

19. The children ______ spend too much time watching TV.
A. mustn’t
B. ought to not
C. shouldn’t
D. Both B and C are correct

20. If you have a bad headache, you ______ see the doctor.
A. had better
B. must
C. ought to
D. should