1. You shouldn't eat so many hamburgers. They're not good for you.
2. You don't have to study at the weekends, except when you have exams.
3. You needn't worry. Everything will be OK.
4. You mustn't use your mobile phone in class.
5. Diana looks happy. She must have heard some good news.
6. I can't have left my mobile phone at school on Friday afternoon - I had it on Friday night.
7. It can rain tomorrow.