Question

All mammals, without any exception, are characterized by

• A. viviparity and biconcave red blood cells
• B. extra abdominal testes and four chambered heart
• C. heterodont teeth and 13 pairs of cranial nerves
• D. a muscular diaphragm and milk producing glands

Answer 1

The correct option is D a muscular diaphragm and milk producing glands

• Viviparity is not exhibited by egg-laying mammals
• Testes are abdominal in some egg-laying mammals and in elephants
• Humans are mammals with 12 pairs of cranial nerves
• Mammals typically have heterodont dentition, but this may also be found in other non-mammals such as crocodile.

Diaphragm is a muscular partition separating the thoracic and abdominal cavity. Mammary glands are the milk-producing glands. Diaphragm and mammary glands are the characteristic features of all mammals.