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)

--> Diễn tả hành động xảy ra song song / cùng lúc 

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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EX2: 

2. started

3. decided 

4. was downloading 

5. called 

6. wanted 

7. was waiting 

8. listened 

9. saw 

10. took

EX3: 

2. Lily was wearing her new dress when I met her. 

3. We were watching a film when we heard a strange noise. 

4. When you called me, I was having dinner. 

5. When my dad got home, my sister was listening to music. 

EX4:

2. was watching 

3. were playing 

4. was raining 

5. was your brother doing 

6. was uploading