设 $f(z)$ 在闭路 $C$ 上及其内部解析，$z_0$ 在 $C$ 的内部，则有 ．
A. $\oint_C \frac{f(z)}{\left(z-z_0\right)^2} \mathrm{~d} z=f^{\prime}\left(z_0\right) \oint_C \frac{1}{\left(z-z_0\right)^2} \mathrm{~d} z$ ；
B. $\oint_C \frac{f(z)}{\left(z-z_0\right)^2} \mathrm{~d} z=\oint_C \frac{f^{\prime}(z)}{z-z_0} \mathrm{~d} z$ ；
C. $\oint_C \frac{f(z)}{\left(z-z_0\right)^2} \mathrm{~d} z=\frac{f\left(z_0\right)}{2!} \oint_C \frac{1}{z-z_0} \mathrm{~d} z$ ；
D. $\oint_C \frac{f(z)}{\left(z-z_0\right)^2} \mathrm{~d} z=\oint_C \frac{f\left(z_0\right)}{z-z_0} \mathrm{~d} z$ ．