# In a triangle $ABC, \; \frac{a}{b^2-c^2} + \frac{c}{b^2-a^2} = 0$, then $B$ is equal to :
( A ) $\frac{\pi}{2}$
( B ) $\frac{2 \pi}{3}$
( C ) $\frac{\pi}{3}$
( D ) $\frac{\pi}{4}$