C

Step 1: Understand the forces at play when a person walks on a rough surface. When a person walks, he exerts a force backwards on the ground through his feet (due to Newton's Third Law: for every action, there is an equal and opposite reaction).
Step 2: By pushing against the ground, the person creates a reaction force according to Newton's third law. This reaction force is what propels him forward due to friction between his shoes and the rough surface. The friction does not keep him moving but instead prevents slipping, allowing him to push off effectively.
Step 3: Therefore, the correct interpretation is that the reaction of the force the man exerts provides him with the forward movement needed to walk.
Conclusion: Option C correctly states that the reaction of the force which the man exerts on the floor keeps him moving.