A mass m is attached to a spring with a spring constant K. If the mass is set into simple harmonic motion by a displacement d from its equilibrium position, what would be the speed, v, of the mass when it returns to the equilibrium position?

A) v = sqrt(md/k)
B) v = sqrt(kd/m)
C) v = sqrtkd/mg)
D) v = d•sqrt(k/m)