Pulsating X-Ray Sources Are Believed to Be

Pulsating X-ray sources are believed to be

A) white dwarf stars with intense magnetic fields; the X-rays are generated by flares like those on the Sun but much stronger.
B) spinning neutron stars in binary systems, emitting X-rays because of mass transfer onto the neutron star from its normal companion.
C) the same as regular (optical) pulsars but observed in X-rays.
D) black holes in binary systems, with an accretion disk around the black hole emitting X-rays.