The common ancestors of birds and mammals were very early (stem)reptiles, which almost certainly possessed three-chambered hearts (two atria, one ventricle). Birds and mammals, however, are alike in having four-chambered hearts (two atria, two ventricles). The four-chambered hearts of birds and mammals are best described as
A) structural homologies. B) vestiges. C) homoplasies. D) the result of shared ancestry. E) molecular homologies.