Read the passage and answer the question.

Most people refer to koalas as koala bears, but they are not. They are marsupials and are in the same family as the wombat. Koalas live in eucalyptus forests in eastern and southeastern Australia. Adult koalas are one of only three mammals that can survive on a diet of eucalyptus leaves. These leaves contain 50% water, requiring them to seldom drink water since they obtain it through the leaves.

Since the koala is a marsupial, the baby crawls into the mother’s pouch as soon as it is born. Baby koalas are called “joeys.” When they are born, they are blind, hairless, and less than one inch long. They remain in their mother’s pouch for the next six months, feeding first on the mother’s milk and then on a substance called “pap” in addition to the mother’s milk. Joeys continue to take their mother’s milk until they are a year old. The young koala will remain with its mother until the appearance of another joey from the mother’s pouch.

Which of the following would be an appropriate heading for the second paragraph of this passage?