If the pair of lines given by $(x^2+y^2) \sin \alpha = (x \cos \alpha - y \sin \alpha)^2$ are perpendicular to each other, then $\alpha$ is equal to :

Question

( A ) $\frac{\pi}{3}$
( B ) $\frac{\pi}{4}$
( C ) $0$
( D ) $\frac{\pi}{2}$