Answer:
A. Force of friction
Explanation:
Find the diagram attached
From the diagram we can see that the force B is acting up on the body along the plane. This force is the force that prevents the body from sliding down the plane. Originally, the body on the line will tend to slide down the incline even without application of a force hence the reason of an opposing force that must act in the opposite direction is counter this motion to make the body be in a state of equilibrium. Hence the required force is force of friction since it is am opposing force acting in the direction opposite to the moving force acting on the body.
