If $\frac{(x+1)^2}{x^3 + x} = \frac{A}{x} + \frac{Bx + C}{x^2 + 1}$, then $\sin^{-1} (A/C)$ is equal to :

Question

( A ) $\frac{\pi}{2}$
( B ) $\frac{\pi}{6}$
( C ) $\frac{\pi}{4}$
( D ) $\frac{\pi}{3}$