A body of mass $$m=0.25\ \text{kg}$$ is moving along the $$x$$ axis under the action of a conservative force. Its potential energy as a function of position $$x$$ is given by $$U(x)=-\frac{100x}{x^2+4}\ \text{J}$$, with $$x$$ in metre. Then

A

force $$F(x)$$ acting on the body at $$x=0$$ is $$25\ \text{N}$$

B

there is stable equilibrium at $$x=2\ \text{m}$$

C

there is unstable equilibrium at $$x=-2\ \text{m}$$

D

the body executes small oscillations with angular frequency $$\omega=0.5\ \text{rad s}^{-1}$$