2 hành động song song trong quá khứ => quá khứ tiếp diễn

1 hành động đang diễn ra trong quá khứ (quá khứ tiếp diễn) thì có 1 hành động khác cắt ngang (quá khứ đơn)

III.

1. saw - were trying

2. was walking - felt

3. were driving - appeared

4. was she driving - happened

5. was waiting - came

6. invited - was visiting

7. didn't want - was waiting

8. rang - was watching

9. began - was sitting

10. went - were having

IV.

1. came - were watering

2. was talking 

3. was practising - was reading

4. were climbing - visited

5. was talking - entered

6. was making - went

7. was crossing - stepped - fell

8. began - was planting

9. arrived, was writing

III.

1. saw/were trying

2. was walking/felt

3. were driving/appeared

4. was she driving/happened

5. was waiting/came

6. invited/was visiting

7. didn't want/was waiting

8. rang/was watching

9. began/was sitting

10. went/were having

IV.

1. came/were watering

2. was talking 

3. was practicing/was reading

4. were climbing/visited

5. was talking/entered

6. was making/went

7. was crossing/stepped/fell

8. began/was planting

9. arrived/was writing