put the following sentences into passive voice
----- Nội dung dịch tự động từ ảnh -----
1. John wrote this letter.
2. His friend will deliver that letter.
3. He had found the key before they arrived.
4. He hasn't prepared his lesson yet.
5. They didn't leave the report here.
6. We must warn them of danger.
7. People can't hold the meeting in that room.
8. You should follow your father's advice.
9. He is doing his exercises carefully.
10. My mother told us an interesting story.