D. All females give birth to live young
Some Mammals are egg-laying mammals which not give birth to live young. Only two kinds of egg-laying mammals are left on the planet today—the duck-billed platypus and the echidna, or spiny anteater. These odd “monotremes” once dominated Australia, until their pouch-bearing cousins, the marsupials, invaded the land down under 71 million to 54 million years ago and swept them away.
