The point with the greatest potential energy is B.
The potential energy of an object is depends on the relative distance between the object and the ground and its mass. The higher the object is from the ground the greater the potential energy posses.
Potential energy (P.E) = mgh
Where m is the mass, g is the gravity and h is the height from the ground to where the object is.
Since the mass and gravity is constant in this case, only the height will determine the point with the greatest P.E and that point is B.
