Atomic number equals the number of _ or the number of _. * giving

Can someone explain to me how to do this problem ?

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 backward on the person. b. the person's feet push forward on the sidewalk; the sidewalk does not push on the person. c. the person's feet push backward on the sidewalk; the sidewalk pushes forward on the person. d. the person's feet push forward on the sidewalk; the sidewalk pushes forward on the person.

Acar drives toward the right over the top of a hill, as shown below. which arrow represents the centripetal acceleration? w x y z