Complete the sentences with the correct modal verb in italics:
1. You couldn't/mustn't / shouldn't eat so many hamburgers. They're not good for you.
2. You can't have / don't have to /mustn't study at the weekends, except when you have exams.
3. You may not/might not/needn't worry. Everything will be OK.
4. You don't have to/might not/mustn't use your mobile phone in class.
5. Diana looks happy. She can/can have /must have heard some good news.
6. I'm not sure but I can't/couldn't / might not be here tomorrow.
7. I can't/may not/might not have left my mobile phone at school on Friday afternoon - I had it on Friday night.
8. It can/could/ couldn't rain tomorrow.