Alexis and Candace were testing different surfaces to see which one had the least friction. They predicted that the marble, seen above, would travel FASTEST down the ramp when the surface covering had the LEAST friction. Alexis and Candace used rocks, plywood, and velcro to cover the ramp. They let the marble go, not pushing it, but letting gravity pull the marble to the bottom of the ramp.

What is/are the responding variable(s) in the experiment?











A) the different types of ramp coverings


B) how fast the marble moved down the ramp


C) ramp height, the marble, and using gravity


D) pushing or not pushing the marble down the ramp