$$
\frac{d^{2}x}{dy^{2}} \; = \; ?
$$
$
(a) -\left(\dfrac{d^{2}y}{dx^{2}}\right)^{-1}\left(\dfrac{dy}{dx}\right)^{-3}
$
$ (b) \left(\dfrac{d^{2}y}{dx^{2}}\right)\left(\dfrac{dy}{dx}\right)^{-2}
$
$
(c) -\left(\dfrac{d^{2}y}{dx^{2}}\right)\left(\dfrac{dy}{dx}\right)^{-3}
$
$
(d) \left(\dfrac{d^{2}y}{dx^{2}}\right)^{-1}
$