Momentum and Newton's laws of motion — practice question

For a raindrop of mass $m$ descending vertically at speed $v$, the resultant force $F$ is described by $F = mg - kv^2$ in which $k$ is a constant and $g$ represents the acceleration of free fall. As the raindrop falls, it finally attains a constant (terminal) velocity. Which graph shows how the terminal velocity of the raindrop varies with mass $m$?