1. They went home after they had finished their study.
2. Yesterday when I arrived to the party, they had already came home.
3. After  the  guests  had left,she went back into the living room and switched
  off the light.
4. On arrival at home I found that she had just left just a few minutes before.
5. Before he went to bed, he had done his homework.
6. When they got to the place, the man had died 
7. He had done nothing before he saw me.
8. He thanked me for what I had done for him.
9. I was sorry that I had hurted him.
10. After they had gone , I sat down and rest

*Note: Sau after dùng QKHT

Trước before dùng QKHT

Hành động xảy ra trước dùng QKHT

Hành động xảy ra sau dùng QKĐ

1. They (go) home after they (finish) their study

→ went/ had finished

2. Yesterday when I (arrive) to the party, they (already go) home.

→ arrived/ had already gone

3. After the guests (leave) , she (go) back into the living-room and (switch) off the light.

→ had left/ went/switched

4. On arrival at home I (find) that she (just leave) just a few minutes before.

→ found/ had just left

5. Before he (go) to bed, he (do) his homework.

→ went/had done

6. When they (get) to the place, the man (die)

→ got/ had died

7. He (do) nothing before he (see) me.

→ had done/ saw

8. He (thank) me for what I (do) for him.

→ thanked/ had done

9. I (be) sorry that I (hurt) him.

→ was/had hurt

10. After they (go) , I (sit) down and (rest)

→ had gone/ sat/rested