глаголы в начале задания: can, cannot,may,must,mustn't,should.

1. must (но лучше бы have to) 2. may 3. had to (must не употребляется в прошедшем времени) 4. had to 5. could 6. can 7. had to 8. had to, couldn't 9. mustn't 10. may 11. can't 12. shouldn't 13. couldn't 14. needn't  15. shouldn't 16. was able to (=could) 17. cannot 18. needn't 19. have to 20. must1. must 2. can't 3. can't 4. must 5. shouldn't (needn't)