1. arrived-was still sleeping

2. went-were having

3. was having-stopped

4. were crossing-saw

5. saw-was standing

6. was reading-learnt-did

7. were playing-came

9. was-worked

10. was sitting-saw

11. woke up- were telling

12. was waiting-arrived

13. wanted-choosed

14. studied-phoned

15. found-was looking for

1. arrived / was sleeping 

2. went / were having

3. was having / stopped

4. were crossing / saw

5. saw / was standing 

6. was reading / was learning / was doing 

7. were playing / came

8. rang / was taking 

9. was /worked

10. was sitting / saw

11. woke up / told 

12. was waiting / arrived 

13. wanted / chose

14. studied / phoned

15. found / was looking for

=> -chia ở quá khứ đơn hoặc quá khứ tiếp diễn 

       -Qúa khứ đơn : khi hành động đó xảy ra và đã kết thúc ở quá khứ 

       -Hành động đang xảy ra ( chia ở quá khứ tiếp diễn ) bất chợt hành động khác xen vào ( chia ở quá khứ đơn )

Structure : 

- Qúa khứ đơn : S + was/were + adj/Noun

                          S + V – ed

- Qúa khứ tiếp diễn : S + was(n't) / were(n't) + V-ing

CHÚC BẠN HỌC TỐT !

Xin ctlhn ạ ! thanks tus nha :)