A Donkey Pulls a Crate Up a Rough, Inclined Plane

Multiple Choice

A donkey pulls a crate up a rough, inclined plane at constant speed. Which one of the following statements concerning this situation is false?

A) The gravitational potential energy of the crate is increasing.
B) The net work done by all the forces acting on the crate is zero joules.
C) The work done on the crate by the normal force of the plane is zero joules.
D) The donkey does "positive" work in pulling the crate up the incline.
E) The work done on the object by gravity is zero joules.