During a demonstration of Newton’s laws of motion, a student used the setup shown in Figure 1. The student flicked the index card with a fingertip, and the coin fell straight down into a plastic cup as shown in Figure 2. A: A falling body accelerates at a constant speed.

B: The motion of an object is constantly changing due to magnetic forces.
C: The force friction causes an object in motion to move faster.
D: An object remains at rest, or at a constant speed, an unbalanced force acts on it.