37. A block of mass M on a horizontal surface is connected to the end of a massless spring of spring constant k. The block is pulled a distance x from equilibrium and when released from rest, the block moves toward equilibrium. What coefficient of kinetic friction between the surface and the block would allow the block to return to equilibrium and stop?
(A) 2Mgkx2
(B) Mgkx
(C) 2Mgkx
(D) 2kxMg