Which explanation describes the forces involved for a person to walk down the sidewalk?
A.
The person's feet push backward on the sidewalk; the sidewalk pushes forward on the person.
B.
The person's feet push forward on the sidewalk; the sidewalk pushes forward on the person.
C.
The person's feet push backward on the sidewalk; the sidewalk pushes backward on the person.
D.
The person's feet push forward on the sidewalk; the sidewalk does not push on the person.