Mammals have all of the following characteristics except:​

A) ​a diaphragm involved in breathing
B) ​a four-chambered heart
C) ​a merging of nasal and mouth cavities
D) ​milk from mother's mammary glands

Diaphragm

A muscular and membranous partition separating the thoracic cavity from the abdominal cavity, playing a critical role in the respiratory process by contracting and expanding to allow breathing.

Four-Chambered Heart

An anatomical feature of the heart, consisting of two atria and two ventricles, which efficiently separates oxygenated and deoxygenated blood, seen in mammals and birds.

Mammary Glands

Specialized organs in mammals that produce milk to nourish newborn offspring, present in both sexes but usually functional only in females.