The prouct of the length of perpendiculars from the foci on any tangent to the ellipse $\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$ is :

Question

( A ) $a^2 - b^2$
( B ) $b^2$
( C ) $\sqrt{a^2 +b^2}$
( D ) $a^2$