[单选题]
One 20-year-old twin brother cyp4n ;lf+g b;takes a space tr.e++6 b2 (drprjac qitip with a speed of 0.80c for 30 years according to a clock on the spaceship. Upon returning to the Earth, what is his own age and the r+d+6eij 2r.q( acpbtage of the Earth-based twin brother?
