On his way to class, a student on a skateboard is accelerating on a downhill stretch. Which of the following statements is true? (Select all that apply.) A. The skateboarder's acceleration is perpendicular to the net force.
B. The skateboarder is moving in the direction of the net force.
C. The skateboarder's acceleration is in the direction of the net force.
D. The skateboarder is subjected to a net external force in the direction of motion.