Here are the sentences rewritten in passive voice:
The flowers are watered by Mother in the evening.
She was shown the way by a boy.
A box of fruit will be sent to us by them.
The horses are often driven to the fields by the boys in summer.
The book has been translated into 25 languages by them.
Cameras cannot be used in the museum.
A letter is being dictated by the manager to her secretary right now.
Dr. Johnson was being interviewed by someone.
This room has not been used by anybody for ages.
This cathedral was built by French priests.