Đổi các câu sau thành câu bị động 
6. People use milk to make butter.
7. You must keep your room tidy.
8. Nobody saw her at the party last night.
9. The government has not changed the regulation.
10. She didn't introduce me to her mother.
11. Someone is cutting the grass now.
12. Someone ought to repair this window.
13. They couldn't use the key because it was very small.
14. He was explaining the title of the book when we got into the library.
15. Her husband didn't love her