Hawaiian Honeycreepers (Birds), Consisting of 50 Species, Some of Which

Hawaiian honeycreepers (birds) , consisting of 50 species, some of which are now extinct, represent a much more diverse lineage than Hawaiian thrushes.Honey creepers have a remarkable variation in bill morphology, whereas Hawaiian thrushes exhibit far less morphological variation.Bill morphology is strongly linked to the resources available for these birds to eat.This suggests that _______ in honey creepers may have occurred as a result of _______.

A) sexual dimorphism; leks
B) allopatric speciation; hybrid zones
C) sexual selection; monogamous pair bonds
D) adaptive radiation; dietary specialization
E) adaptive radiation; poor dispersal ability