1. decided- was (yesterday-QKĐ)
2. was learning- called- asked (Hành động đã dang xyả ra (QKTD) thì hành động khác xen vào (QKD) )
3. will cancel- is (câu điều kiện loại 1)- will do
4. am flying (at present-HTTD)-go- have lived (for 60 years-HTHT)
5. has taught (since-HTHT)- moved
6. will contact- finishes
7. understand
8. doesn't study- will fail (Câu điều kiện loại 1: If+S+HTĐ, S+will/can/.. V)
9. was fixing- was cooking (At 5 p.m yesterday: thời gian cụ thể, hai hành động không liên quan đến nhau- đều chia QKTD)
10. was- played (when i was 5 tuổi- QKĐ)- don't play- like- playing (nowadays: ngày nay-HTĐ)
11. will wait- finishes
12. arrived- was dacing- drinking
13. Have you ever heard (ever-HTHT)
14. have you been- have been (for 3 months- HTHT)
15. was searching- was- didn't find (last night)
16. isn't
17. will be
18. have you seen- went (since-HTHT)
19. spend- playing (spend time/money+ V-ing: dành thời gian/tiền bạc làm gì)
20. requires- need- to spend