Which of These Statements Is NOT True About the Center

Multiple Choice

Which of these statements is NOT true about the center of mass of a binary star system?

A) The center of mass is always on the line joining the two stars.
B) The center of mass is simultaneously a focus of the ellipse of each star's motion.
C) The center of mass is always more distant from the more massive star.
D) The center of mass can move with respect to the more distant background stars.