Answer:
C. The person's feet push backward on the sidewalk; the sidewalk pushes forward on the person.
Step-by-step explanation:
Newton's third law states that for every action, there is equal and opposite reaction. It is also known as action-reaction principle. A person is able to walk on sidewalk by pushing the sidewalk backwards. Then, the sidewalk pushes the person's feet forward.
Action: The person's feet push backward on the sidewalk.
Reaction: The sidewalk pushes forward on the person.