Here are the sentences rewritten in passive voice:

1. A good idea has been given by them for this project.
2. I was not helped by them.
3. Cookies will be bought by them for Christmas next week.
4. The temple was reconstructed by people in 1903.
5. Why was the temple visited by many students of literature last week?
6. TV was being watched by my father.
7. Her exercise has been done by Mary since 5 p.m.
8. This road must be finished by them this year.
9. It was believed by people that Mary passed the exam.
10. Mary was believed to have passed the exam.