Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species of birds. Recently, they have been reclassified as a single species, the yellow-rumped warbler, under the biological species concept. Which of the following observations would support this reclassification

A) The two forms are observed to interbreed successfully where their habitats overlap.
B) The two forms live in similar habitats.
C) The two forms have many genes in common.
D) The two forms have similar food requirements.
E) The two forms are very similar in coloration.