设 $M=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \frac{\sin x}{1+x^2} \cos ^4 x \mathrm{~d} x$ ，
$$
\begin{aligned}
& N=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}\left(\sin ^3 x+\cos ^4 x\right) \mathrm{d} x, \\
& P=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}\left(x^2 \sin ^3 x-\cos ^4 x\right) \mathrm{d} x
\end{aligned}
$$
则
$\text{A.}$ $N < P < M$
$\text{B.}$ $M < P < N$
$\text{C.}$ $N < M < P$
$\text{D.}$ $P < M < N$