When the C magnetic ring set in the top of the B, A, B and C are at rest, the size of the force between B and C for G, corresponding to the distance for h3, A and B between the size of the force 2G, corresponding to the distance for h2, according to the magnetic ring between the repulsive force decreases with distance, and the distance is h2. Repulsion with the decrease in distance and increase the principle can be seen, h1> h2, h2 The choice of B.