As you know from the last classes, in English, many sentences use the active form of the verb. The performer of the action, or the agent, comes first and is the subject of the verb that follows. The receiver of the action is the object of the verb, and it comes after the verb. For example,
The builders took down the shelves.The builders painted the wallIn these sentences, the builders are the agent of the action. The wall and the shelves are the object of the verb, the receiver of the action. The verb is in the active form.
The passive form is used when we want to focus attention on the receiver of the action, not on the agent of the action. In this case, the receiver of the action becomes the subject of the verb, which is now in the passive form. For example,
The shelves were taken down.The wall was painted
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After reading try the general quiz, quiz one, quiz two and quiz three.