Ответ:
1. The food was eaten by the dog.
2. John was hit by the car.
3. The letter was written by Jenny.
4. "E.T." was directed by Steven Spielberg.
5. The question was answered by Julie.
6. The money were stolen. (можно дописать by the boy, но обычно, если не важно, кто это сделал, то есть без имени, а просто мальчик, то не пишется, но если напишешь, ошибкой не будет).
7. Some trees has been planted (опять же, можно дописать by gardener).
8. The test was taken (by children).
9. The new movie was watched (by several people).
10. "Twelfth Night" was written by Shakespeare.