Which of the following groups is characterized by three major categories: egg-laying, pouched, and placental?

The group characterized by the three major categories of egg-laying, pouched, and placental is Mammalia. This classification highlights the diversity within mammals based on reproductive strategies.

Egg-laying mammals, known as monotremes, include species like the platypus and echidna, which lay eggs instead of giving birth to live young. Pouched mammals, or marsupials, such as kangaroos and koalas, give birth to relatively undeveloped young that continue their development in a pouch. Finally, placental mammals are those that carry their young in a uterus where they are nourished via a placenta until they are ready to be born.

This classification underscores the evolutionary adaptations of mammals, demonstrating how different reproductive strategies have emerged in response to environmental pressures and parental investment. The other groups listed do not share this specific classification scheme.