The correct option is: (a)
Explanation:
To be a mammal the presence of hair and milk or mammary gland is must, but presence of 7 cervical vertebrae and 12 pairs of cranial nerves are also additional mammalian characteristics. The monotremes make up by far the smallest sub-class of mammals, With just three species, found in Australia, Tasmania, and New Guinea. One of these is the duck-billed platypus, and the remaining two are the echidnas, or spiny anteaters. The duck-billed platypus and the spiny anteater are mammals that lay eggs rather than give live birth to young ones. The platypus has a bill or beak like a duck, fur like a mammal and webbed feet. It lays eggs that look like reptile eggs. Its young one are fed from the mother's mammary glands. The spiny anteater's covering looks like that of the porcupine. It has a long tongue to catch insects and a bill. It lays several eggs which it keeps in a pouch on its side.
