Evidence Obtained Over the Last Few Years Indicates That a Quasar

Evidence obtained over the last few years indicates that a quasar is MOST probably:

A) the remnant core of an exploding star or supernova.
B) the focused image of a distant galaxy by the gravitational lens effect of a closer galaxy.
C) evidence of very intense star-building activity in certain distant dust and gas clouds.
D) the central nucleus of very distant, very active galaxy.