A、To stay safe. B、To keep company. C、To save energy. D、To protect the young. A浏览四个选项，从选项中的to do形式可推测，此题与目的有关。题干问的是根据说话者所言，为什么有些鸟

Winter in many places is very cold. There is lots of snow around, and the ground freezes, which can make life difficult for animals. People in cold places live in warm houses and have learned to adapt. What do animals do? (22) There are three main ways that animals survive the cold in winter; sleep, adapt or migrate.
    Some animals, such as bears, frogs and snakes, sleep all winter. They sleep very deeply and need little or no food. (23) While sleeping, their body temperature drops, and their heart beat slows down. To prepare for this before winter, these animals eat extra food to become fat, which gives them the energy they need while they sleep.
    Other animals adapt. For example, by staying active in winter. It is often hard for them to find food. (24) So some animals, such as mice, collect extra food before winter, and hide it. When winter comes, they return to the hiding places to eat the food. Some animals grow thicker fur, or live in tree holes or underground to stay warm.
    Some birds migrate by flying to a warmer place for the winter, where they can find more food. Some fly very long distances, including one kind of bird that flies from the remote north of the world, all the way to the distant south. (25) Some birds fly in groups for safety, while others fly alone.
Questions 22 to 25 are based on the passage you have just heard.
22. What does the speaker say about animals in winter?
23. What do we learn about animals that sleep through winter?
24. How do animals like mice adapt to the severe winter?
25. Why do some birds fly in groups when migrating, according to the speaker?