设 $$
\begin{aligned}
M & =\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \frac{(1+x)^2}{1+x^2} \mathrm{~d} x, \\
N & =\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \frac{1+x}{e^x} \mathrm{~d} x \\
K &=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}(1+\sqrt{\cos x}) \mathrm{d} x ，
\end{aligned}
$$
则 $M, N, K$ 的大小关系为