What Do We Expect to Be the Relationship Between the Number

What do we expect to be the relationship between the number of active galaxies we detect and the number of active galaxies that actually exist?

A) The energy output from active galaxies is so large that it is easy to detect them. Thus, we believe we have detected all that exist.
B) The nuclei of many active galaxies are hidden by dust in the accretion disk. Thus, we expect the actual number to be much greater than the observed number.
C) We cannot detect active galaxies unless the jets are pointed more or less toward Earth. The jets point toward Earth in only a few cases, so we expect the actual number to be greater than the observed number.
D) Active galaxies are created in galaxy collisions. But galaxy collisions occurred only in the early universe and are no longer occurring. The active galaxies all died off while their light was traveling to Earth.