Correct Answer: All kinds of things are left in the school by children.

Solution : The correct choice is the fourth option.

Passive voice is the voice in which the object experiences an action rather than the person who performs the action. Hence, the object in the active sentence becomes the subject in the passive voice.

The structure of the passive voice is:

"Object  + was + past participle of the main verb + by + agent of action"

Therefore, the correct passive form is: "All kinds of things are left in the school by children."