7.84 For any function $y=f(x)$, in the same Cartesian coordinate system, the graphs of the functions $y=f(x-1)$ and $y=f(-x+1)$ are
(A) symmetric with respect to the $x$-axis.
(B) symmetric with respect to the line $x=1$.
(C) symmetric with respect to the line $x=-1$.
(D) symmetric with respect to the $y$-axis.
(China High School Mathematics League, 1989)
[Solution] Since the graphs of the functions $f(z)$ and $f(-z)$ are symmetric with respect to the line $z=0$, the graphs of the functions $f(x-1)$ and $f(-x+1)$ are symmetric with respect to the line $x-1=0$, which is the line $x=1$.
Therefore, the correct choice is $(B)$.