Ornithologists Visiting an Island Find Two Species of Bird That

Ornithologists visiting an island find two species of bird that appear nearly identical except for bill size. Which of the following is the most likely explanation for their discovery?

A) There is natural random variability.
B) Coevolution of the two species has resulted in resource partitioning between the species.
C) Mutations and natural selection have resulted in an inferior species with defective bills.
D) Sexual selection has taken place.
E) The birds need camouflage for protection from predators.