One question about SHM

Since kinetic energy KE is proportional to the square of speed v^2, options C and D are mutually exclusive.

KE + PE = constant (where PE is the potential energy of the system)
i.e. KE = constant - PE = constant - Kx^2 (where K is another constant, and x is the displacement)
hence, KE vis which x is a pararbolic form.

But v is proportional to the square-root of KE. By taking square-root on both sides of the equation doesn't give a parabolic curve.