The tangent at $\mathrm{P}(5 \cos \theta, 3 \sin \theta)$ on the ellipse $\frac{\mathrm{x}^{2}}{25}+\frac{\mathrm{y}^{2}}{9}=1$ meets the auxiliary circle $\mathrm{x}^{2}+\mathrm{y}^{2}=25$ at two points $\mathrm{A}$ and $\mathrm{B}$.
If AB subtends $90^{\circ}$ at the centre of the ellipse, then
(a) $\sin ^{2} \theta=\frac{9}{16}$
(b) $\sin ^{2} \theta=\frac{16}{25}$
(c) $\mathrm{e}^{2}=\left(1+\sin ^{2} \theta\right)^{-1}$
(d) $\mathrm{e}^{2}=\left(1+\cos ^{2} \theta\right)^{-1}$