8. The domain of the function $f(x)$ is $x \in \mathbf{R}$, and $x \neq 1$, it is known that $f(x+1)$ is an odd function. When $x>1$, the decreasing interval of $f(x)$ is ( ).
A. $\left[\frac{5}{4},+\infty\right)$
B. $\left(1, \frac{5}{4}\right)$
C. $\left[\frac{7}{4},+\infty\right)$
D. $\left(1, \frac{7}{4}\right]$
8. C. Let $x+1=t$, then $-x+1=2-t, \therefore f(t)=-f(2-t)$, i.e., $f(x)=-f(2-x)$. When $x>1$, $2-x<1$, thus $f(x)=-f(2-x)=-\left[2\left(x-\frac{7}{4}\right)^{2}+\frac{7}{8}\right]$.