Which of the Following Is Not True of Quasars

Which of the following is not true of quasars?

A) Some quasars are more than a thousand times more luminous than the Milky Way.
B) Quasars were more common in the past.
C) Quasars are powered by the energy radiated by matter falling into a central black hole.
D) Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.
E) Some quasars can change their brightness every few hours.