A beach ball weighs less than a bowling ball primarily because the beach ball has less mass. Weight is the force exerted by gravity on an object, which is directly related to its mass. In this case, despite the beach ball having air inside it, its overall mass is less than that of the bowling ball, resulting in a lower weight.
So, the correct choice is: The beach ball has more mass. (Please note, however, that the reasoning should actually state that the bowling ball has more mass than the beach ball).
If phrased correctly, the answer would be: The bowling ball has more mass.