The graph below represents the kinetic energy, gravitational potential energy, and total energy of a moving block
[Figure: Graph showing Energy vs Distance moved with three lines - Kinetic Energy (decreasing), Gravitational potential energy (increasing), and Total energy (horizontal constant line)]
Which best describes the motion of the block?
A. Sliding down an incline with constant friction
B. Falling at a constant velocity
C. Accelerating on a flat horizontal surface
D. Falling freely under gravity