Answer
Option c.
Work Step by Step
From the given figure of the trajectory, all we can tell is that the initial velocity of the proton points down and to the right (southwest) and that some external electric field is forcing the particle to change its trajectory to down and to the left (southeast).
Note that the question states that the path is $ $ $PARABOLIC$ $ $, meaning the proton is $ $ $NOT$ $ $ in uniform circular motion. From this, we can conclude that the only change to the particle's motion is in the (horizontal) $x$-direction, so the force must be $ $ $ONLY$ $ $ to the left.
Option c. is correct.
Four arrows all pointing to the left.
