1) Personal Passive
When we put an object of an active sentence into passive, it becomes subject of the passive sentence.
The professor explained the students the exercise.
The professor explained the exercise to the students.
The students were explained the exercise.
The exercise was explained to the students.
We sometimes use a pronoun for “the students” or “the exercise” in its subject form (here: they/it).
They were explained the exercise.
It was explained to the students.
We very often leave out the by-agent in the passive sentence (here: by the professor).
2) Impersonal Passive – It is said …
The phrase It is said … is an impersonal passive construction. We often use it in news.
Passive sentence – version 1:
It is said that children are afraid of ghosts.
Passive sentence – version 2:
Children are said to be afraid of ghosts.
The correct active sentence would be:
Active sentence: People say that children are afraid of ghosts.