=>
1. were playing (at 3 o'clock yesterday -> QKTD)
2. were you doing/was watching (at 8 last night -> QKTD) 
3. saw/was talking (when QKĐ, QKTD)
4. came/were cooking
5. was drinking (between 8 and 9 last night -> QKTD)
6. were crossing/saw (As QKTD, QKĐ)
7. were having (while QKTD)
8. knocked/were watching
9. was listening/was reading
10. phoned/was taking
11. were playing
12. was reading/was cooking
1. went home/had finished (QKĐ after QKHT)
13. had already seen (said -> lùi thì)
14. had already begun
15. hadn't eaten
16. asked/came
17. sat/rested
18. watched/had done (before QKĐ, QKHT)
19. went
20. was/was
21. had ever seen

1. were playing 
2. were you doing/was watching 
3. saw/was talking 
4. came/were cooking
5. was drinking 
6. were crossing/saw
7. were having 
8. knocked/were watching
9. was listening/was reading
10. phoned/was taking
11. were playing
12. was reading/was cooking
1. went home/had finished 
13. had already seen 
14. had already begun
15. hadn't eaten
16. asked/came
17. sat/rested
18. watched/had done 
19. went
20. was/was
21. had ever seen