19. The rain stopped last week. (同上)

18. I opened the door an hour ago. (同上)

17. He couldn’t go to school because it rained heavily. (同义句)

16. You shouldn’t make him do such boring work. (改为被动语态)

15. We have known him for a week. (改为一般过去时)

14. Why not go to work by bus? (同义句)

13. Mr Wang has kept going to work on foot for twenty years. (同义句)

12. He is a helpful teacher. Every student is grateful to him. (合并)

11. He is very strong. He can carry the big box. (改为简单句)

10. The doctor was too tired to operate on the patient. (改为复合句)