1. The graph of the function $y=\arccos x(-1 \leqslant x \leqslant 1)$ is symmetric about the $y$-axis and is denoted as $c_{1}$, and the graph of $c_{1}$ symmetric about the line $y=x$ is denoted as $c_{2}$. Then the equation of $c_{2}$ is ( . ).
- (A) $y=\cos x(0 \leqslant x \leqslant \pi)$
(B) $y=\arcsin x(-1 \leqslant x \leqslant 1)$
(C) $y=-\cos x(0 \leqslant x \leqslant \pi)$
(D) None of the above answers is correct
i. (C).

From the problem, we know that the equation of $c_{1}$ is $y=\arccos (-x)(-1 \leqslant x \leqslant 1)$, and $c_{2}$ is the inverse function of $c_{1}$ (since $c_{1}$ and $c_{2}$ are symmetric with respect to the line $y=x$), so the equation of $c_{2}$ is $y=-\cos x(0 \leqslant x \leqslant \pi)$.