Question

All mammals without any exception are characterised by

• A. viviparity and biconcave red blood cells
• B. extraabdominal testes and a four chambered heart
• C. heterodont teeth and 12 pairs of cranial nerves
• D. a muscular diaphragm and milk producing glands

Answer 1

Answer: (D)

a muscular diaphragm and milk producing glands

Answer 2

Vivipary is shown by all mammals except monotremes (Platypus and echidna) All mammals do not have Biconcave $RBCs$, example Camel has ovaloid $RBCs$. Elephants do not have extra abdominal testes and four-chambered hearts are not exclusive to Mammals. Heterodont teeth and $12$ cranial nerves are both not exclusive to mammals as they can be found in other animal groups too. Muscular diaphragm and mammary glands are the only characteristics having no exceptions and are exclusive to mammals. So the correct answer is '$A$ muscular diaphragm and milk-producing glands'.