Ans: C
Consider the equation of the straight line, we have
$\begin{array}{rcl}
\dfrac{\log_5 y -2}{\log_5 x-0} & = & \dfrac{0-2}{-4-0} \\
2\log_5 y -4 & = & \log_5 x \\
\log_5 y^2 -\log_5 5^4 & = & \log_5 x \\
\log_5\left(\dfrac{y^2}{625}\right) & = & \log_5 x \\
\dfrac{y^2}{625} & = & x \\
\dfrac{y^2}{x} & = & 625
\end{array}$
