5. were having/ came ( hành động came xen ngang hành động having dinner )

6. was talking/ saw

7. left/ called

8. was getting/ slipped/ broke 

9. fell/ hurt/ was riding 

10. was walking/ saw

11. was studying

12. were they doing

13. met 

14. taught ( dạy ) 

15. didn't go ( quá khứ đơn, dấu hiệu : yesterday )

16. was working ( dấu hiệu: at that time )

17, gave 

18.  were playing 

19. buying 

20. was doing ( 2 việc xảy ra cùng lúc vào thời điểm  nói)

ex 4

1. before i passed the exam, i had worked very hard

2. after considering what to study, I decided....

3.  before going to bed, she had written a letter

4. after having checked the prices, he bought...

5. before taking some medicine, he felt...

6. after arguing, they fired.....

7. before having a facial, she had gone....

8. after she had faced the matter, she went...

9. before writing the assignment, we read the book 

5. were / having come.

6. was talking / saw.

7. left / called.

8. was getting / slipped / broke.

9. feel / hurt / was riding .

10. was walking / saw.

11. was studying .

12. were they doing.

13. met.

14. taught.

15. didn't go.

16. was working 

17. gave.

18. were playing.

19. buying.

20. was doing.

Exercise 4:

1. Before I passed the exam, I hard worked very hard.

2. After considering what to study, I decided to major Maths.

3. Before going to bed, she had written a letter.

4. After having checked the prices, he bought a cassette.

5. Before taking some medicine, he felt a little better.

7. Before having a facial, she had gone out for a walk .

sorry mik chỉ làm dc tới đây thôi mong bạn thông cảm