一定质量的理想气体，从状态A经过状态B变化到状态C，如图所示，图中BC是平行于横轴的直线，已知气体在状态A时的体积为V_A=0.2m³．

    Wouldn't it be funny if your mum said to you, "It's time for bed, honey. It's almost November!" Well, if you were a baby bear, your mother might let you know it's time to go into a deep sleep around October.

    That "deep sleep" is called "hibernation (冬眠)". When it gets cold, bears have to go into hibernation. By taking this long sleep, they can get through the cold months when the food, like berries (浆果) and nuts, cannot be found easily.

    Have you ever heard someone say that they are as hungry as a bear? Bears need to eat a lot of food before hibernating. They eat so much that they may put on forty pounds of fat in a week. During the winter "bears will live off the fat stored in their bodies. Bears are able to do that because their bodies use a lot less energy during hibernation. Their heartbeats slow down, their breathing slows down, and their body temperature drops.

    If you were going to sleep all winter, wouldn't you want to be in a safe and protected place? That is what a bear wants, so it looks for a cave to sleep in. It makes a bed using grass, leaves and twigs (嫩枝). The bear usually starts to hibernate as early as October and doesn't wake up until April or May. By the time the bear wakes up, it will have lost much of the fat. But spring time will bring much food to enjoy until it is time to hibernate again in the autumn.