In Playing a Game of "Logic" with His Dad, John

In playing a game of "logic" with his dad, John hears dad say "If dogs are animals or plants, and we have deduced that dogs are not animals, then dogs must be what?" John answers, "Well, they must be meat eaters then because I've never seen a dog that looked like a plant." We might conclude from John's answer that John is

A) mentally retarded
B) at Piaget's formal-operational stage
C) at Piaget's concrete-operational stage
D) displaying adolescent egocentrism