设 $F(x, y, z)$ 连续可微，$F_x \cdot F_y \cdot F_z \neq 0$ ，方程 $F(x, y, z)=0$ 可确定连续可微的隐函数 $z=z(x, y), y=y(z, x), x=y(y, z)$ ，则（ ）。
A. $\frac{\partial z}{\partial y} \cdot \frac{\partial y}{\partial x} \cdot \frac{\partial x}{\partial z}=-3$ ；
B. $\frac{\partial z}{\partial y} \cdot \frac{\partial y}{\partial x} \cdot \frac{\partial x}{\partial z}=3$ ；
C. $\frac{\partial z}{\partial y} \cdot \frac{\partial y}{\partial x} \cdot \frac{\partial x}{\partial z}=-1$ ；
D. $\frac{\partial z}{\partial y} \cdot \frac{\partial y}{\partial x} \cdot \frac{\partial x}{\partial z}=1$ ．