Suppose a Wall Divides a Playground,and Twenty Balls Lie on the Ground

Suppose a wall divides a playground,and twenty balls lie on the ground on the east side,while forty balls lie on the west side.If a child on the east side of the wall always tosses a ball over the wall at the same time a child on the west side tosses a ball over the wall,then:

A) equilibrium has been established.
B) all balls will eventually end up on one side.
C) equilibrium will be established once thirty balls are on each side.
D) this system can never reach equilibrium.
E) none of the above