Question #5 - My answer was marked wrong on this test. I need the correct answer and explanation for test corrections.

5. While traveling in its elliptical orbit around the Sun, Mars gains speed during the part of the orbit where it is getting closer to the Sun. Which of the following can be used to explain this gain in speed? a. As Mars gets closer to the Sun, the Mars-Sun system loses potential energy and Mars gains kinetic energy. b. A component of the gravitational force exerted on Mars is perpendicular to the direction of motion, causing an acceleration and hence a gain in speed along that direction. c. The torque exerted on Mars by the Sun during this segment of the orbit increases the Mars-Sun system's angular momentum. d. The centripetal force exerted on Mars is greater than the gravitational force during this segment of the orbit, causing Mars to gain speed as it gets closer to the Sun