A) Maize gave a beautiful speech at the Veteran's Day Memorial.
Active voice is when the subject of the sentence is actually doing the action of the main verb. In this sentence Maize is the subject and she is the one giving the speech. Active voice is preferred in writing because it helps to make the writing clearer and more direct.
Passive voice is when the subject of the sentence is really receiving the action of the verb, not doing it. For example, in option C the subject of the dependent clause is "race". The verb phrase is "were organized". The race did not organize itself. Someone else organized the race. This dependent clause is written in passive voice.