If ghosts can walk through walls and glide down stairs, why don’t they fall through the floor?

ghosts float, because they cannot stand on anything made of any type of substance

explanation:

ghosts ca pass through objects at will but you will never see a ghost standing on anything

answer; i believe that the correct answer is (d) a very small amount of mass

convex lenses are thicker at the middle. rays of light that pass through the lens are brought closer together (they converge). a convex lens is a converging lens. when parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.