What Appears to Be the Central Energy-Generating System or "Engine

What appears to be the central energy-generating system or "engine" that is producing prodigious amounts of energy in the centers of galaxies, active galaxies, and quasars?

A) steady series of supernova explosions, the late evolutionary stages of massive stars
B) rapidly rotating core of matter, where friction between it and the surrounding matter causes tremendous heat and energy output
C) supermassive black hole, where matter is compressed on falling into the hole and heated to extremely high temperatures
D) There is no central "engine" in these sources. Their high gravity has focused radiation from many sources beyond them by gravitational lensing and they thus appear to be very bright.