If an object is working against gravity, that means gravity must have the opposite sign of the object (this is why we see objects slow down at their peak height and return to us if we throw them in the air!). If the object is working with gravity, though, they must both be moving in the same direction, therefore gravitational acceleration would be the same sign as the velocity (positive or negative depending on how you define your axes).
Therefore, your answer should be C. Different sign + or - on the acceleration.
I hope this helps!