Dưới đây là cách viết lại các câu từ yêu cầu của bạn:

16. Alice's strange ideas astonished everybody.
Everybody was astonished by Alice's strange ideas.

17. You will catch a cold if you don’t keep your feet dry.
Unless you keep your feet dry, you will catch a cold.

18. Henry regretted buying a second-hand car.
Henry wishes he hadn’t bought a second-hand car.

19. They have sold that old house at the end of the road.
That old house has been sold.

20. “Don’t bite your nails,” said Mrs. Rogers to her son.
Mrs. Rogers advised her son not to bite his nails.

21. “I’ve seen this film 3 times, Mary,” said George.
George told Mary that he had seen this film 3 times.

22. John missed the ferry because his car broke down.
If his car hadn’t broken down, John wouldn’t have missed the ferry.

23. Jane is a better cook than Robert.
Robert can’t cook as well as Jane.

24. Please do not smoke in this area of the restaurant.
Customers are requested not to smoke in this area of the restaurant.

25. “Have you had enough for lunch?” the landlady asked me.
The landlady asked me if I had had enough for lunch.