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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1. I was shopping when Linda called me.

2. My brother was doing his homework at 9 o'clock.

3. He was eating lunch when we arrived.

4. Was she living in Hue at that time?

5. She was playing the guitar at 6 p.m.

6. Was she typing a letter when her book went into the meeting room?

7. While she was watching TV, she heard the doorbell.

8. Was she studying English at 8 p.m yesterday?

9. She saw an accident while she was watching television.

10. What was your little brother doing at this time yesterday?

11. The doorbell rang while she was eating lunch. 

12. Were your friends drinking juice when you arrived? 

13. What was Asley doing while her sister was going to Ha Noi?

14. At 9 p'clock last Sunday, I was doing my homework.

`color{orange}{~MiaMB~}`