1. fell, was painting - Harry fell off the ladder while he was painting the ceiling of his room. 2. bought, cost - We bought the house in 2003. At that time it cost 150,000. 3. was not interested - Dad was not interested in buying a new car. 4. was waiting, arrived - My sister was waiting for me at the airport terminal when I arrived. 5. was reading, heard, were playing - A few nights ago, I was reading a book when suddenly I heard a noise outside. A few teenagers were playing loud music. 6. was still burning, arrived - The fire was still burning when the first firefighters arrived at the scene. 7. was looking, came across - My brother was looking for a job when he came across an interesting ad in the newspaper. 8. heard, turned, saw, was - I heard someone call my name. I turned around and saw my dad standing at the back of the queue. I was so surprised. 9. was wearing, saw - My sister was wearing a bright summer dress when I saw her at the performance. 10. started, was, came - I started preparing dinner at 4 pm and I was still at it when my wife came home. 11. broke, was picking up, cut - Our housekeeper broke the vase. As she was picking up the pieces, she cut her middle finger. 12. realized, were driving - We suddenly realized that we were driving in the wrong direction. 13. was - She was a great skier when she was young. 14. met, was doing - I met an old friend in town while I was doing the shopping. 15. were playing, decided - While the children were playing with others, my husband and I decided to have a cup of coffee. Giải thích: Các động từ trong ngoặc được điền vào thì quá khứ đơn hoặc thì quá khứ tiếp diễn phù hợp với ngữ cảnh câu. Thì quá khứ đơn được sử dụng để diễn tả một hành động đã xảy ra trong quá khứ và đã kết thúc. Thì quá khứ tiếp diễn được sử dụng để diễn tả một hành động đang xảy ra trong quá khứ. Các câu đã được dịch sang tiếng Việt để hiểu rõ nghĩa của câu.