32. Suppose that the potential energy of a particle constrained to move along the x-axis can be described by the function U(x)=kx2- ax, where both k and a are positive constants. Stable equilibrium points, about which the particle oscillates, are located at (A) x = 0 only (B) x = only 2a (C) x= only -*) k (D) x = 0 and α k =α 2α (E) x = 0 and k x=29 K