The ratio of limiting friction and normal reaction is known as _____________________?

A. three forces acting at a point will be in equilibrium
B. three forces acting at a point can be represented by a triangle, each side being proportional to force
C. if three forces acting upon a particle are represented in magnitude and
direction by the sides of a triangle, taken in order, they will be in equilibrium
D. if three forces acting at a point are in equilibrium, each force is proportional to the sine of the angle between the other two
E. none of the above

A. balance each other
B. cannot balance each other
C. produce moment of a couple
D. are equivalent
E. none of the above