Active voice is when a sentence is written so that the subject is performing the action, as opposed to the verb acting upon the subject, as in passive voice. Since the sentences are already in passive voice, they could be rewritten in active voice as:
1) In my neighborhood, developers are building many new apartment houses.
2) Our plans were changed abruptly when we recieved her message.
3) After the soup was served, they served the turkey.
In passive voice, the verb generally comes before the noun it relates to, whereas in active voice, the noun comes before the verb it relates to. Ex. I pet the dog (active) vs. The dog was pet by me (passive)
