4. The graph of the inverse function of $y=\frac{a-x}{x-a-1}$ is symmetric about the point $(-1,4)$. Then the real number $a$ equals ( ).
A. 2
B. 3
C. -2
D. -3
4. B. Given $y=\frac{a-x}{x-a-1}=-1-\frac{1}{x-(a+1)}$, the center of symmetry is $((a+1),-1)$. The center of symmetry of its inverse function is $(-1,(a+1)) \Rightarrow a+1=4 \Rightarrow a=3$.