Which sentence correctly uses the active voice? A. Reinforced by Joe this afternoon was the side of the cabin. B. The side of the cabin will be reinforced this afternoon by Joe. C. Joe will reinforce the side of the cabin when he comes this afternoon. D. The side of the cabin would be reinforced this afternoon by Joe.

The answer is C.

Explanation:

Active voice basically means that there is a subject performing the action given by the verb, there also has to be an object upon which this action is performed. (I am making a cake.)

Contrary to that passive voice means that the object of an active sentence has become a subject. (The cake is being made.)

We can see that the verb has changed its form to past participle.

Regarding your question, we have Joe (subject) who is supposed to reinforce (verb) the side of the cabin (object).

Whenever a sentence follows the pattern of subject, then verb, then object, it is in active voice, so the answer is C.