Why Do Highway Departments Sometimes Pile Huge Boulders near the Base

Why do highway departments sometimes pile huge boulders near the base of a sloping road cut?

A) to prevent gullying of the sloping road cut
B) to keep vegetation from growing on the sloping road cut
C) to prevent water from getting into the slope
D) to prevent slumping of the road cut by loading the toe of the potential slump
E) to prevent damage to the road cut from collisions with erratic drivers