Answer: C: my parents painted the house that summer.
Explanation: a sentence is in active voice when the action is performed by the subject of the sentence. It is in passive voice when the subject receives the action of the verb (and the direct object becomes the subject). From the given sentences, the one that is in active voice is the corresponding to option C, because the subject (my parents) is performing the action, while the direct object (the house) is receiving the action of the verb (painted).
