Công thức thì QKTD 

(+) S + was/were + Ving 

(-) S + was/were+ not + Ving 

(?) Was/Were +S +Ving? 

--> Diễn tả hành động đang xảy ra ở 1 thời điểm nào đó trong quá khứ 

--> Diễn tả hành động đang xảy ra thì có hành động khác chen vào (while / when)

DHNB: at + giờ + thời gian trong QK, at this time + thời gian trong QK, ...

Công thức thì QKĐ (V: to be)

(+) S + was/were + ... 

(-) S + was/were + not ... 

(?) Was/Were + S ... ? 

S số ít, I, he, she, it + was

S số nhiều, you, we ,they + were

Công thức thì QKĐ (V: thường)

(+) S + V2/ed 

(-) S + didn't + V1 

(?) Did + S+ V1?

DHNB: ago, last (year, month ...), yesterday, in + năm QK, ...

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5. went / had / met 

6. were playing / hurt 

7. were they doing / was

8. was taking / rang 

9. was / rang 

10. walked/ was working 

11. was / was shining / were singing / was walking / met 

12. was living / started

13. got / were waiting 

14. was / was always leaving 

15. visited / saw / spent 

16. were you standing / came 

17. lived / were 

18. were listening 

19. left / was snowing 

20. was working / met 

`color{orange}{~MiaMB~}`