1. We arrived after David had gone home.
- Thì QKĐ + after + thì QKHT.
2. We had had lunch before taking look around the shops.
- Thì QKHT + before + thì QKĐ.
- Before + V-ing(cùng chủ ngữ).
3. When we got out of the office, the flight had gone out.
- When + thì QKĐ, thì QKHT.
4. By the time we started our work, she had explain everything clearly.
- By the time + thì QKĐ, thì QKHT.
4. Before my mother came home, my father had watered all the plants in the garden.
- Before + thì QKĐ, thì QKHT.