A sled slides down a hill, reaches the level surface, and eventually comes to a stop. Which fact ultimately explains why the sled stops?
A. The presence of an unbalanced force causes an object to move forward at constant velocity
B. The presence of an unbalanced force (e.g. friction) causes a moving object to stop
C. The presence of inertia causes a moving object to stop
D. The natural tendency of any object is to ultimately stop
