Ответ:
11. Mike wrote two letters yesterday.
Two letters were written by Mike yesterday.
12. The government supports endangered species.
Endangered species are supported by the government.
13. The builders are reconstructing the house.
The house is being reconstructed by the builders.
14. Has John finished his project?
Has John's project been finished?
15. My mother will bring us some sweets.
Some sweets will be brought to us by my mother.