8 graders - Passive Voice

You are now studying the Passive Voice in your English classes. Please remember that you've already learnt this content in Portuguese. It will be similar. Let's see, in Portuguese you say:
 A Maria come a maçã.                    O Manuel comeu a maçã.

Here you have two active sentences where someone acts in an action, correct? And you have the "poor" apple that suffers that action. Are you with me?

In the Passive Voice your aim is to stress out what suffered the action, and not the person that acts. That's why is passive!

So, you have to pick a maçã and place it as a Subject in the passive sentence, and a maria as a passive agent introduced with by.
We are missing something...what about the verb?

Well, in English, as well as in Portuguese you have an auxiliar verb - to be, that in the passive has to be always in same tense as the sentence in the active voice. Meaning that if the active sentence is in the past simple the verb to be has to be in the past simple, if it is in the present continuous, the verb to be has to be in the present continuous. Confused?!

The main verb has to appear, always, in the Past Participle.

So, the conclusion is:
A maçã é comida pela Maria.      A maçã foi comida pelo Manuel.

Now, examples in English:

Peter reads this book.
This book is read by Peter.

Carol washed her car.
Carol's car was washed by her.

Sue feeds the cat.
The cat is fed by Sue.

Someone opened the door.
The door was opened.

http://www.englisch-hilfen.de/en/exercises/active_passive/sentences_simple_past.htm

http://www.englisch-hilfen.de/en/exercises/active_passive/sentences_simple_present.htm