The only sentence that contains a verb in the passive voice is the third one.
Many enslaved people were rescued by Harriet Tubman.
You can recognize the passive voice by the word order in a sentence. The object always goes first, because in the passive voice, the object become the subject: WHO? Many enslaved people
then you put the auxiliary verb (to be) in the same tense as the main verb of the sentence, in this case the simple past tense: were rescued
and lastly you add by whom was the action preformed: by Harriet Tubman.
