18. have to
19. have to
20. musn't use
21. mustn't
22. have to
23. haven't to
24. must
25. have to
26. mustn't
27. have to
28. have to
29. mustn't
30. doesn't have to
31. don't have to
32. must
33. mustn't
34. has to
35. must / don't have to