A spaceship moves away from Earth at constant velocity 0.60c, according to Earth observers. In the reference frame of the spaceship,

(a) Earth moves away from the spaceship at 0.60c.
(b) Earth moves away from the spaceship at a speed less than 0.60c.
(c) Earth moves away from the spaceship at a speed greater than 0.60c.
(d) The speed of Earth cannot be accurately measured because the reference frame is moving.
(e) The speed of Earth is not constant.