阅读下列短文，根据短文内容，从短文后各题所给的A、B、C、D四个选项中，选择最佳选项。
Koala Joey
Far away in Australia, a koala sits high in a eucalyptus tree. She grips a branch with the rough pads and sharp claws on her paws. In her pouch (小袋) she hides something special—her baby.
At birth the baby koala, called a joey, does not look like his furry mom. He is pink and bald（无毛的）and as small as a jellybean. Although he cannot see, he moves his legs and crawls. He smells milk and, without any help, starts to feel his way to his mother's pouch. Five minutes later he slips (滑) inside.
Inside the pouch, the joey drinks his mother's milk and grows. His eyes open. His ears form, and he hears his mother's calls. Soon thick fur covers his body. By the time the joey is ready to explore the world, he looks like his mother.
At five months old, the joey peers out of his pouch. He eats a special soft food from his mother called pap. When the joey eats pap, he gets bacteria（细菌）from his mother's stomach in his tummy too. He will need the bacteria to eat eucalyptus leaves, like grownup koalas do.
In another month, the joey leaves the pouch for the first time. He clings（贴着）to his mother's belly while she climbs in the treetops. By the time he is eight months old, the joey no longer fits in his mother's pouch. But he still drinks her milk.
Now, for a few hours each night, the joey climbs on his mother's back for a ride. While riding piggyback, he reaches for eucalyptus leaves. Just like mom, he nips (咬) off leaves and chews them. The leaves have plenty of water in them, so koalas rarely go to the ground for a drink. When the joey is about one year old, his piggyback days are over. Now he climbs to the treetops by himself. On each of his front paws, he has two thumbs opposite his three fingers. He can grip branches and grab leaves. The young koala spends more and more time away from his mother. He no longer drinks her milk. He dozes (打瞌睡，打盹) alone on tree branches. Soon he will move to another tree and live on his own.
