When you coast down a hill on a bike you move faster and faster. then when you keep coasting on a level surface, you eventually stop moving. what cause you to stop?

a. no force is acting on your bike on the level surface, so it stops moving.
b. after you reach the bottom of the hill, you run out of energy, so you stop moving.
c. friction between the tires and the ground is an unbalanced force that change your motion.
d. gravity affects you when you move downhill, but there is no gravity when you move on a level surface.