Answer
D.
Work Step by Step
$x=ky^2$ can be further executed to bring it back to proper form with an isolated $y$.
$x=ky^2$
$y^2=x/k$
$y=\sqrt {\frac{x}{k}}$ (note that because the graph only draws quadrant I, so $k$, $x$ and $y$ are both positive. making this transition appropriate)
As $x$ becomes larger, $x/k$ also increases in value, but because they are under a square root, they are increasing at a decreasing rate. D fits this description.
