$$y = \cot^{-1}\left(\frac{1 - 3x^2}{3x - x^3}\right) \Rightarrow \frac{dy}{dx} =$$

A

$$-\frac{3}{1 + x^2}$$

B

$$\frac{3}{1 + x^2}$$

C

$$\frac{3}{1 - x^2}$$

D

$$-\frac{3}{1 - x^2}$$