Answer:
c. arrow's push against the bowstring.
Explanation:
Newtons third law of motion describe the relationship between action and reaction forces. Thus when the action force is applied by the bowstring against the arrow, a reaction to this force is supplied by the arrow's push against the bowstring.
If these two forces are not equal and opposite, the arrow would not move as expected. The elastic property of the bowstring propels the arrow at a rate which is due to the potential energy it has gained due to the stretching force.