방정식 $e^ {xyz} + \ln (xyz) =3$ 에서 $\displaystyle \left (\frac{\partial z} {\partial x} \right) \bullet \left (\frac{\partial z} {\partial y} \right)$ 는?

• ①$\displaystyle \frac{z} {x}$
• ②$\displaystyle \frac{z^2} {xy}$
• ③$\displaystyle \frac{z^2} {x}$
• ④$\displaystyle \frac{z} {y}$