Some animals sleep in wintertime because the weather can be very cold and it is difficult for them to find food. They can sleep for a long time (from autumn to spring). This kind of winter sleep is called "hibernation". If an animal moves about a lot, it needs food. Hibernating animals do not need to eat much because they are not moving about. Their hearts beat very slowly and they also breathe slowly. They find a place that is sheltered from bad weather and they are out of danger. Their body fat keeps them live and warm. Some animals, such as bears, may wake up from their hibernation on warm winter days and then quickly go back to sleep again when they see the snow is still thick on the ground. When the weather becomes warmer in spring, the animals wake up for food. What keep them live in winter
A. Food they store． B. Their body fat. C. The snow．