Автор - ГIOJLNHA
16. This book was written in the 19th century [by him].
17. Tennis was being played from four till five [by them].
18. A number of important experiments have been made in this laboratory [by them].
19. Central Africa was explored in the 19th century [by Livingstone].
20. All the trees had been planted by the middle of autumn [by us].
21. This play will be staged at the beginning of next season [by them].
22. The story has been forgotten [by them].
23. Have the rules of the game been explained to you [by anybody]?
24. My skates haven't been brought back [by them].
25. Corrections are usually made in red ink [by teachers].
То,что в скобках,в принципе можно не писать.