In an experiment, identical objects are placed on a glass slab, and a piece of sandpaper, as shown in the image. One end of both surfaces is raised 100 mm and the objects placed on them are observed. The ends are raised in increments of 100 mm until one of the objects begins to move. What does this experiment demonstrate? A) Friction depends on the surface. B) Friction is independent of the surface. C) Friction is applicable to tilted surfaces only. D) Friction depends on the object more than the surface.