直线 $x+\left(a^2+1\right) y+1=0$ 的倾斜角的取值范围是
A. $\left[0, \frac{\pi}{4}\right]$
B. $\left[\frac{3 \pi}{4}, \pi\right)$
C. $\left[0, \frac{\pi}{4}\right] \cup\left(\frac{\pi}{2}, \pi\right)$
D. $\left[\frac{\pi}{4}, \frac{\pi}{2}\right) \cup\left[\frac{3 \pi}{4}, \pi\right)$