If $a>b>0$ thenthe maximum value of $\frac{a b\left(a^{2}-b^{2}\right) \sin x \cos x}{a^{2} \sin ^{2} x+b^{2} \cos ^{2} x}$ in $\left(0, \frac{\pi}{2}\right)$ is
(A) $a^{2}-b^{2}$
(B) $\frac{a^{2}-b^{2}}{2}$
(C) $\frac{a^{2}+b^{2}}{2}$
(D) none of these