In The $\beta$ Lyrae System, the More Massive Star Is the Dimmer Star

In the $\beta$ Lyrae system, the more massive star is the dimmer star. How could this be?

A) The more massive star is probably a red giant. As it has expanded, its temperature and luminosity have both decreased, as expected.
B) The more massive star has evolved to become a neutron star with a consequent reduction in luminosity.
C) The more massive star has pulled mass from its companion to form an accretion disk, thus cloaking some of its luminosity and appearing dimmer.
D) The smaller star has pulled some of the bright outer layer off the more massive star, thus increasing its own brightness at the expense of its more massive companion.