Help please

The author thinks that since big houses had narrower floorboards, the narrow floorboards were a status symbol. B is able to strengthen the argument since it eliminates an alternative cause. Perhaps the narrow floorboards were simply cheaper, and since bigger houses have a greater amount of floor area to cover, the main reason that big houses used the narrower boards were that it was simply much cheaper given their large surface areas. B tells us this is not the case.