Ans: C
Let $z=\dfrac{ky^3}{x}$, where $k$ is a non-zero constant. Then, we have
Let $z=\dfrac{ky^3}{x}$, where $k$ is a non-zero constant. Then, we have
$\begin{array}{rcl}
z & = & \dfrac{ky^3}{x} \\
k & = & \dfrac{xz}{y^3} \\
\dfrac{1}{k} & = & \dfrac{y^3}{xz}
\end{array}$
Therefore, $\dfrac{y^3}{xz} $ must be constant.
