1. The performance must be over as there are many people leaving the theatre.2. I don't believe that he said it. He can’t have said such a thing. 3. I am sure they knew everything about it. Mary must have told them. She can't keep her word. 4. I am sure that she did not do anything of the kind. They must have taken her sister for her. 5. It is impossible that they should have refused to help you. They can’t have broken their promise.6.Perhaps it was true, I am not sure. She might (OR could) have been ashamed to tell you the truth. 7. Can you really mean it? 8. There is no doubt that it was all prepared beforehand. He must have been watching you. 9. It is impossible. They can’t have left already. I was watching the door of the house.

в 6 возможнo might/could 6.Perhaps it was true, I am not sure. She might (OR could) have been ashamed to tell you the truth   may тоже возможно