Rougher surfaces have more friction between them than smoother surfaces.  Having read the above passage, choose the right answer to the following question (choices are the sandpaper and the glass table or or the sandpaper and the gravel. ):   A piece of sandpaper was rubbed across a glass table, then the sandpaper was rubbed across some gravel. The friction will be less between the sandpaper and the glass table or or the sandpaper and the gravel.?
Answer:
the sandpaper and the glass table or