1. You should stop thinking about bad things.
2. You shouldn't drink so much cola.
3. Can I take this?
4. I can swim under the water
5. He can't play the piano.
6. We must do our homework every day
7. You must do housework
8. She shouldn't being so shy
9. You can't kill people
10. They can play volleyball
11. You must buy thing if you don't like it