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.