If $\;y=e^{nx}\;$ , then $\;(\large\frac{d^{2}y}{dx^{2}}) (\large\frac{d^{2} x}{dy^{2}})\;$ is equal to :

Question

$(a)\;\;n e^{nx} \qquad(b)\;n e^{-nx}\qquad(c)\;1\qquad(d)\;-n e^{-nx}$