1. Was waiting - arrived 

2. Were you doing

3. Did you go

4. were you driving - happened

5. took - wasn't looking

6. didn't know

7. saw - was trying

8. was walking - heard - was following - started

9. wanted

10. dropped - was doing - didn't break

11. Fell - was sleeping

12. Was - was watching

13. Was walking - saw - stopped - had

14. Hurt - was working

15. Were they doing - came

16. Were you sleeping - went 

Thì QKTD diễn tả một hành động đang xảy ra thì có hành động khác xen vào.

1. Jenny …………was waiting………… (wait) for me when I …………arrived………… (arrive)
2. “What …were you doing………………… (you/do) at this time yesterday” “I was asleep”.
3. “………Did you go…………… (you/go) out last night?” “No, I was too tired”.
4. How fast ………were you driving…………… (you/ drive) when the accident …………happened………… (happen)?
5. Sam ………… took………… (take) a picture of me while I ………wasn’t looking …………… (not/ look).
6. We were in a very difficult position. We ………didn't know…………… (not/ know) what to do.
7. I haven’t seen Alan for ages. When I last …………saw………… (see) him, he …………was trying………… (try) to find a job.
8. I …………was walking………… (walk) along the street when suddenly I …………heard………… (hear) footsteps behind me. Somebody …………was following………… (follow) me. I was scared and I (start) …………started………… to run.
9. When I was young, I …………wanted………… (want) to be a pilot.
10. Last night, I ………droppe…………… (drop) a plate when I …………was doing………… (do) the dishes. . Fortunately, it …………didn't break………… (not break) up.
11. Jessica …………fell………… (fall) asleep while she …………was sleeping………… (read) books.
12. The television …………was………… (be) on, but nobody …………was watching………… (watch).
13. I …………was walking………… (walk) along the road when I …………saw………… (see) Dan. So I …………stopped………… (stop) and we (have)had a chat.
14. I ………hurt…………… (hurt) my back while I …………was working………… (work) in the garden.
15. What ………Were they doing …………… (they/do) when the teacher …………come………… (come) into the room?
16. …………Were you sleeping………… (you/sleep) when the alarm clock …………went ………… (go) off?