10. The rescue operation, which was arranged by a charity organization, was a success.
11. Brenda is a friend whom I went on holiday with.
12. This is Mr. Smith whose son Bill plays in our team. 
13. Her book, which became a best-seller, was published last year.
14. This is the bank which we borrowed the money from.
15. I told you about a person who is at the door.
16. Jack, whose car had broken down, had to take a bus.
17. I lent you a book which was written by one of my friends.  
18. Some boys who were arrested have been released.
19. You could imitate native speakers because your pronunciation is not good.  
20. This is the village in which I was born.
``
Thay thế cho 
- người: who
- vật: which
- sở hữu cách: whose

``
Mệnh đề quan hệ:
- xác định:
+ không có phẩy
+ mệnh đề phía sau đại từ quan hệ không thể lược bỏ
+ có chủ ngữ chưa xác định
- không xác định:
+ có dấu phẩy
+ mệnh đề phía sau đại từ quan hệ có thể lược bỏ
+ có chủ ngữ đã xác định (Tên người, địa điểm nổi tiếng, sở hữu,...)