A Small Lead Sphere of Mass M Is Hung from a Spring

A small lead sphere of mass m is hung from a spring of spring constant k. The gravitational potential energy of the system equals zero at the equilibrium position of the spring before the weight is attached. The total mechanical energy of the system when the mass is hanging at rest is

A) −kx2.
B) − kx2.
C) 0.
D) + kx2.
E) +kx2.