A crate of weight $W$ is pushed up an incline by a force of magnitude $F$. There is significant friction between the ramp and the crate. The crate starts at the very bottom of the incline and is moved all the way to the top of the incline, along the distance $C$ shown in the diagram. The ramp has horizontal length, A, vertical height B, and diagonal length C.
Which one of the following is a correct expression for the magnitude of the work done by gravity during the crate's motion?