Suggest a 'C'

Everything else being equal, a wider tire will reduce gas mileage, not increase it; the wider tire has greater rolling resistance (and greater traction due to a larger contact patch), and also a greater rotational inertia that takes more energy to speed up and slow down. For smallish changes in tire size, the differences are small, and other factors can also come into play such as the composition of the rubber and often the overall diameter of the tire.

There are good reasons why you don't see anything other than skinny tires on Tour de France bicycles.