2. In a regular $n$-sided pyramid, the range of the dihedral angle formed by two adjacent side faces is
A. $\left(\frac{n-2}{n} \pi, \pi\right)$
B. $\left(\frac{n-1}{n} \pi, \pi\right)$
C. $\left(0, \frac{\pi}{2}\right)$
D. $\left(\frac{n-2}{n} \pi, \frac{n-1}{n} \pi\right)$
2. A Suppose the base $A_{1} A_{2} \cdots A_{n}$ (a regular $n$-sided polygon) of a regular $n$-sided pyramid $S-A_{1} A_{2} \cdots A_{n}$ is fixed, and the vertex $S$ moves along a line $l$ that passes through the center of the base and is perpendicular to the base.

Draw $A_{2} H \perp S A_{1}$ at $H$, and connect $H A_{n}$. Since all the lateral faces of the regular $n$-sided pyramid are congruent, $H A_{n} \perp S A_{1}$, so the plane angle of the dihedral angle between two adjacent lateral faces is $\angle A_{2} H A_{n}$.
When $S$ moves along the line $l$ towards the extreme position (the center of the base), $\angle A_{2} A_{1} A_{n}$ tends to a straight angle $\pi$;
When $S$ moves along the line $l$ towards infinity, the regular $n$-sided pyramid tends to a regular $n$-sided prism, $\angle A_{2} H A_{n}$ tends to $\angle A_{2} A_{1} A_{n}=\frac{n-2}{n} \pi$. In summary, $\quad \frac{n-2}{n} \pi<\angle A_{2} H A_{n}<\pi$.