A certain system has potential energy given by the function \[U(x)=-a{{x}^{2}}+b{{x}^{4}}\]with constants, a, b > 0. Which of the following value of x is an unstable equilibrium point?

• A. 0
• B. \[\sqrt{a/2b}\]
• C. \[-\sqrt{a/2b}\]
• D. \[\sqrt{a/b}\]