Final answer:
True, marsupial young spend more time developing outside the mother's body in the protective pouch, unlike placental mammals.
Step-by-step explanation:
Marsupial young do indeed spend more time developing outside the mother's body than inside, which makes the statement (a) True. Marsupials, including kangaroos and koalas, give birth to very immature embryos that continue their development in the mother's pouch, a specialized external feature that provides nutrition and protection. This development process is considered an adaptation to reduce risks for the mother, although it means the embryo is more fragile at birth compared to placental mammals that have a more extended development inside the uterus nourished by a placenta.