A Heavy Box Is at Rest on an Inclined Plane

A heavy box is at rest on an inclined plane. The box begins to slide down the inclined plane when a small force is applied to the box. The force is removed as soon as the box begins to slide. The speed of the box increases as the box slides down the inclined plane.Which of the following is the most likely cause of this increasing speed?

A) The force of gravity on the box is less when the box is not moving than when the box is moving.
B) The force of gravity on the box is greater when the box is not moving than when the box is moving.
C) The force of friction on the box is less when the box is not moving than when the box is moving.
D) The force of friction on the box is greater when the box is not moving than when the box is moving.