In the equation Wa/r generally used in the rolling frictional calculations, what does each stands for?

• A. P is the force, W is weight of the body, r radius and a coefficient of rolling friction all in normal powers
• B. P is the force in nano Newton, W is weight of the body, r radius and a coefficient of rolling friction
• C. P is the force, W is weight of the body in kg, r radius and a coefficient of rolling friction
• D. P is the force, W is weight of the body, r radius cm and a coefficient of rolling friction