What group of mammals have (a) embryos that spend more time feeding through the placenta than the mother's nipples, (b) young that feed on milk, and (c) a prolonged period of maternal care after leaving the placenta?

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Eutherian mammals have a well-developed placenta that allows for a prolonged period of gestation and nourishment of the developing embryo. After birth, the young feed on milk produced by the mother's mammary glands, and many eutherian species exhibit prolonged periods of maternal care and nurturing of the offspring. Marsupials (B) have a shorter gestation period and give birth to relatively undeveloped young, which complete their development outside of the womb within a marsupial pouch, where they nurse on milk produced by the mother. Monotremes (C) lay eggs and have a shorter period of maternal care and nursing of the offspring.

What Group of Mammals Have (A) Embryos That Spend More