Two identical charged spheres suspended from a common point by two massless strings of lengths I, are initially at a distance d (d < < ) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity v. Then v varies as a function of the distance x between the spheres, as : (a) v x x (b) v x x (c) v x x - (d) v x x