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: thường)

(+) S + V2/ed 

(-) S + didn't + V1 

(?) Did + S+ V1?

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

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6. saw / was driving 

7. was waiting / was doing 

8. arrived / were having 

9. were playing / were going 

10. were having / was sleeping 

11. took / was feeding

12. were playing / went 

13. were cleaning / was doing

14. was doing / phoned 

15. were waiting / arrived 

`color{orange}{~MiaMB~}`

`6.` saw - was driving 

`7.` was waiting - was doing 

`8.` arrived - were having 

`9. ` were playing - were going 

`10.`  were having - was sleeping 

`11.`  took - was feeding

`12.`  were playing - went 

`13.`  were cleaning - was doing

`14.` was doing - phoned 

`15.` were waiting - arrived 

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`-` when /while + QKĐ, + QKTD

`->` Diễn tả hành động đang xảy ra thì hành động khác xen vào 

`-` QKTD + while + QKTD

`->` Diễn tả 2 hành động xảy ra cùng 1 lúc

`-` QKĐ:

S+ V2/V-ed +O

`-` QKTD:

S+ was/were + V-ing +O