X-Ray Bursters Emit Occasional and Intense Bursts of X-Rays on Top

X-ray bursters emit occasional and intense bursts of X-rays on top of a steady low-level X-ray emission. These bursts of X-rays are believed to be caused by

A) material from a companion star pulled into an accretion disk around a black hole, and, consequently, periodic clumps of material falling from the disk into the black hole and being compressed produce the X-rays.
B) material transferred onto the surface of a neutron star, causing the neutron star to collapse suddenly into a black hole.
C) material transferred onto the surface of a neutron star in a binary system, then subsequently ignited in a thermonuclear explosion that leaves the neutron star intact to repeat the process.
D) material transferred onto the surface of a white dwarf in a binary star system, producing a thermonuclear explosion at the surface while leaving the white dwarf intact to repeat the process.