The Major Surprise About Cygnus A, One of the First

The major surprise about Cygnus A, one of the first three sources of strong radio emission detected by Grote Reber in the late 1930s, when examined with a large optical telescope, was that it:

A) was at the center of our galaxy.
B) was a supernova remnant.
C) corresponded to no optical source at all.
D) was a relatively faint yet very distant object at optical wavelengths.