on its rough, unglazed bottom; the other on its smooth, glazed side (See figure below). When the teacher slowly raised the plane to a steeper angle, one student shouted, "the angle makes one cup moves faster and another slower." Which of the following is the most appropriate action from the teacher to help the student correct his causality? A. Setting up the plywood at a fixed angle and demonstrating that the cup is not moving on the plywood when it is on its rough unglazed bottom, and it is moving while on its smooth glazed side B. Directly telling the student that he is wrong and giving him the right answer that it's the contact surface that makes the difference C. Replacing the cup with a cube which has the same smoothness on 6 faces and repeating the lab. D. Covering the plywood with a piece of foil paper and repeating the lab