please answer change the active voice to passive voice

1. the book is discussed by them.
2. the door is closed by the teacher.
3. the answer will be changed (by him).
4. cake was being made (by me).
5. biology is being studied (by her).
6. the problem will be being talked about by mary.
7. the salt has been  taken (by me).
8. some flowers are planted by my parents.
9. the twin mountains were climbed by john.
10. my bird is killed (by you).