The Chandra X-Ray Observatory has detected X rays from a star system that contains a main-sequence star of a spectral type B6. The X-ray emission is strong and fairly steady, and no sudden bursts have been observed. Which of the following statements are reasonable conclusions about this system?

a. The main-sequence star orbits either a white dwarf or a neutron star.
b. The main-sequence star orbits either a neutron star or a black hole.
c. The main-sequence star must orbit a white dwarf.
d. The main-sequence star is emitting X rays.
e. Gas from the main-sequence star makes an accretion disk around another object.
f. The main-sequence star must orbit a black hole.
g. Some time in the next few decades, this system will undergo a nova explosion.
h. The main-sequence star must orbit a neutron star.