Explain the theory and practice of two methods of measuring astronomical distances that are based upon different physical principals?

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.

Which subatomic particle has a negative charge

Abar magnet cut in half will form a total ofpoles.a)fourb)eightc)two