Why Would a Female Song Bird Choose to Mate with a Male

Why would a female song bird choose to mate with a male that has a large song repertoire?

A) females tend to select traits that are well developed to judge fitness of a male.
B) females judge by feather color and voice of the male.
C) a long song allows the female to study the male for any physical defects before mating.
D) immature males have a long varied song where older, less fit males will have a short song.
E) females only judge fitness by physical appearance, not song repertoire.