Trả lời:

11.The agreement was signed by six country.

12.I was helped by a stranger.

13.The post is delivered on Sundays.

14.The report must be written by your manager.

15.The Christmas party is being organized by the children

16.The sliver medal has been won by the French team.

17.The guard dogs were being trained by a woman.

18.This game can be played by people of all ages.

19.The match was being watched by a large crowd.

20.A reply was sent by the headmaster.

Chúc học tốt !

11. The agreement was signed by six countries.

12. I was helped by a stranger 

13.The post isn't delivered on Sundays.

14. The report must be written by your manager.

15. The Christmas party is being organized by the children

16. The silver medal has been won by the French team.

17. The guard dogs were being trained by  a woman

18. This game can be played by people of all ages.

19. The match was being watched by a large crowd.

20. A reply was sent by the headmaster.