Four Small Spheres, Each of Mass M, Connected by Four

Four small spheres, each of mass m, connected by four nonconducting strings to form a square with side d, are placed on a horizontal, nonconducting, frictionless surface. Balls A and B, placed on adjacent corners, each have a charge Q; balls C and D are uncharged. The maximum speed of balls C and D after the string connecting balls A and B is cut is

A) 2(kQ²/3md) ².
B) (2kQ²/3md) ².
C) (4kQ²/9md²) ^1/2.
D) (2kQ²/3md) ^1/2.
E) 2(kQ²/3md) ^1/2.