The Major Point of the Discussion of Birdsong Learning in the Text

The major point of the discussion of birdsong learning in the text is that

A) unlike mammals, birds learn only through operant conditioning.
B) it is likely that species evolve their own ways of learning to solve their own unique problems.
C) psychologists now know that the same principles of learning found in mammals also apply to birds.
D) this is the only known example (in any species) of classical conditioning without a CS.