When One Member of a Binary Star System Is a Black

When one member of a binary star system is a black hole, and astronomers detect flickering x-rays coming from the system, where are these x-rays usually coming from?

A) from inside the black hole event horizon
B) from the photosphere of the companion star (the star that is not a black hole)
C) from the singularity
D) from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole)
E) from a distant galaxy that just happens to lie behind the black hole system (astronomers discovered that such x-rays have nothing to do with the black hole)