Turn the following sentences into the passive. Add the agent when necessary.

1. Alfred Hitchcock directed the film.
2. They are building a new house.
3. They were helping the students.
4. People will always remember him.
5. We make cheese from milk.
6. Peter has painted the picture.
7. You must hand in the keys before leaving.
8. The children opened all the windows.
9. The police are going to arrest the two criminals.
10. Scientists have found a new species of butterfly in the Amazon rainforest.