Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes dimmer for about 2 hours. The most likely explanation is that
A) the star is a Cepheid variable.
B) the star is a member of an eclipsing binary star system.
C) the star is periodically ejecting gas into space, every 73 hours.
D) the star is a white dwarf.
Answer: B