4. The symmetric line of the line $f(x, y)=0$ with respect to the line $x-y-2=0$ is
(A) $f(y+2, x)=0$
(B) $f(x-2, y)=0$
(C) $f(y+2, x-2)=0$
(D) $f(y-2, x+2)=0$
C



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