1. B It must be from Paul.
2. B You should go to the dentist.
3. C It could be upstairs.
4. B I have to do my homework.
5. A Would you babysit for me tonight?
6. C You needn’t have done the washing up.
7. C John can’t have watched it.
8. A You mustn’t keep pets in the flat.
9. C Shall I open the door for you?
10. B You needn’t do the shopping.