The correct response is:
The box exerts 10 N of force downward.
This is based on Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. Since the two ropes are exerting a total of 10 N of upward force (5 N from each rope), the box must exert an equal amount of force downward (10 N) to keep the forces balanced and to remain stationary.