`16.` was having - rang -answered 

`17.` saw - was sitting - reading 

`18.` was walking - hurt

`19.` burnt - was cooking 

`20.` fell - was paiting 

`21.` was reading - heard 

`22.` Were you watching 

`23.` was waiting - arrived

`24.` wasn't driving - happened 

`25.` broke - was doing - slipped

----------------

`-` When/ While + QKĐ, QKTD.

-> Diễn tả hành động quá khứ này đang diễn ra thì hành động quá khứ khác xen vào

`-` QKTD + while+ QKTD.

-> Diễn tả 2 hành động quá khứ diễn ra song song nhau.

`-` Quan hệ song hành:

V-ing+ and + V-ing

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, ...

-----------------------------------------------------

16. was having / rang / answered

17. saw / was sitting / reading 

18. was walking / hurt 

19. burnt / was cooking 

20. fell / was painting 

21. was reading / heard

22. Were you watching 

23. was waiting / arrived 

24. broke / was doing / slipped 

`color{orange}{~MiaMB~}`