122 If the line $x=\frac{\pi}{4}$ is intercepted by the curve $C$:
$$
(x-\arcsin \alpha)(x-\arccos \alpha)+(y-\arcsin \alpha)(y+\arccos \alpha)=0
$$

to form a chord of length $d$, the minimum value of $d$ as $\alpha$ varies is
A. $\frac{\pi}{4}$
B. $\frac{\pi}{3}$
C. $\frac{\pi}{2}$
D. $\pi$