A particle of mass m is executing oscillations about the origin on the.\[Y\]-axis with amplitude\[A\].Its potential energy is given as\[U(x)=b{{x}^{4}}\], where \[\beta \] is a positive constant. The \[x\]-coordinate of the particle, where the potential energy is one-third of the kinetic energy, is

• A. \[\pm \frac{A}{2}\]                  
• B. \[\pm \frac{A}{\sqrt{2}}\]
• C. \[\pm \frac{A}{3}\]                  
• D. \[\pm \frac{A}{\sqrt{3}}\]