Hello-
I'm thinking it's C, and I'll explain - don't worry.
Active voice is when the subject performs something on an object. For example:
"Sam ate the cookie."
If you wanted to rewrite the sentence above to be passive, it would look more like this:
"The cookie was eaten by Sam."
The passive voice is telling us what is being done to the object.
All the other options are akin to the active voice, but the sentence "After the walk, the pizza was eaten quickly by Sufyan" more closely resembles the passive example. So I have reason to believe that C is the correct answer.
I hope this answers your question.
-Toremi
