A ball hangs at rest from a string attached to the ceiling. The string pulls up on the ball with a force equal to its weight. The 3d law pair to the upward force of the string on the ball is a(n)... O upward force exerted by the ball on the string O downward force exerted by the ball on the string O upward force exerted by the ball on the earth O upward force exerted by the string on the earth O downward force exerted by the earth on the ball O downward force exerted by the earth on the string