Answer
If C moves farther away from the origin, $F_{net}$ gradually changes in direction to the left of the positive y axis.
The limit of this change is that $F_{net}$ would point directly at B.
Work Step by Step
By symmetry, the x-components of the two gravitational forces on A cancel out and $F_{net}$ is directed in the positive y direction initially.
If C moves farther away from the origin, the gravitational force on A due to C decreases, and $F_{net}$ gradually changes in direction to the left of the positive y axis.
As C continues to moves farther away from the origin, $F_{net}$ continues to move more to the left of the positive y axis. Note that as the distance of C from the origin approaches infinity, the gravitational force on A due to C approaches 0. The limit of this change is that $F_{net}$ would point directly at B.
