Double-Radio Sources, Quasars, and BL Lacertae Objects Are Now Considered

Multiple Choice

Double-radio sources, quasars, and BL Lacertae objects are now considered to be the same basic type of object-an accretion disk producing two oppositely directed jets-but they appear to observers to be very different because

A) the relativistic particles ejected in the double jets are different in each case: electrons in double-radio sources, protons in quasars, and quarks in BL Lacertae objects.
B) they are at different distances from Earth, so one sees more detail and different properties in those that are closer to Earth.
C) they are of different ages.
D) astronomers view them at different angles to the line of the double jets. Face-on to the accretion disk the source will look like a BL Lacertae object, edge-on as double-radio sources, and between these positions a quasar.