A sled starts atop a hill at rest with 3,000 J of potential energy relative to the bottom of the hill. When the sled reaches the bottom of the hill it has 2,000 J of kinetic energy. Why does the sled have less energy at the bottom of the hill than at the top?

A) The hill isn't very steep.
B) Some of the energy is destroyed.
C) Some of the energy is converted to heat.
D) The sled does 1,000 J of work on the hill.