Final answer:
When you stop after running down the stairs, your kinetic energy decreases to zero and your gravitational potential energy remains constant since you are no longer changing your height.
Step-by-step explanation:
When you run down some stairs and stop, your kinetic energy actually decreases because you are no longer in motion. Initially, as you were descending the stairs, your kinetic energy was increasing because your speed was increasing due to gravitational potential energy being converted into kinetic energy. However, once you come to a stop, kinetic energy is reduced to zero. As for the gravitational potential energy, it decreases as well when you move from a higher elevation to a lower one, and it remains constant once you stop since you are not changing your position in the vertical direction any further.
The correct answer to the question would thus be: b) Kinetic energy decreases; Potential energy remains constant. This is because, upon stopping, you are no longer in motion (kinetic energy is zero) but your height relative to a reference point (like the bottom of the stairs) doesn't change anymore (gravitational potential energy is constant).