Answer: Difficult, but I choose C: His conclusion is based on an assertion regarding unfairness, and unfairness is a very subjective concept.
Explanation: The ineffectiveness in Antoine's argument is, in my mind, that he is ignoring the purpose of the gasoline tax increase. The purpose is to limit petroleum consumption, not to increase revenues. The increased revenue, in fact, could be used to lower taxes. While his argument does seem to address fairness, that doesn't apply here. In fact, it would be unfair to add taxes to people who don't consume much petroleum. Furthermore, his plan would do nothing to direcly reduce petroleum consumption. Choice C came closest to this line of thought.