答案：A
留意圓心的坐標
留意圓心的坐標
$\begin{array}{cl}
= & \left( \dfrac{-(-4)}{2}, \dfrac{-(6)}{2} \right) \\
= & (2,-3)
\end{array}$
所以，通過 $(1,2)$ 的直徑的斜率
$\begin{array}{cl}
= & \dfrac{-3-2}{2-1} \\
= & -5
\end{array}$
