16. The waitress who served us was impolite and impatient.  
17. The building which was destroyed in the fire has now been rebuilt. 
18. The people who were arrested have now been released.
19. The bus which goes to the airport runs every half hour.
20. The girl who was injured in the accident is now in hospital.
21. He worked for a woman who used to be an artist. 
22. They called a doctor who lived nearby.
``
Cách làm.
1. Xác định danh từ/... mà cả 2 câu đều có.
2. Xác định nếu từ đó chỉ người/vật/địa điểm/thời gian/...
3. Dùng mệnh đề quan hệ thích hợp:
- Which: vật; người + vật 
- Who: người
- When: thời gian
- Where: địa điểm
-...
4. Nối 2 vế, bỏ từ bị trùng ở câu thứ 2

`-` Who là MĐQH dùng để chỉ về người

`-` Which là MĐQH dùng để chỉ về vật

`16`.The waitress who served us was impolite and impatient

`->` Who `=` The waitress

`17`.The building which was destroyed in the fire has now been rebuilt

`->` Which `=` The building

`18`.The people who were arrested have now been released

`->` Who `=` The people

`19`.The bus which goes to the airport runs every half hour

`->` Which `=` The bus

`20`.The girl who was injured in the accident is now in hospital

`->` Who `=` The girl

`21`.He worked for a woman who used to be an artist

`->` Who `=` a woman

`22`.They called a doctor who lived nearby

`->` Who `=` a doctor

`\text{# TF}`