【正确答案】 D

【答案解析】[听力原文]

Science: Hibernation

Professor: We have been talking about animals" habitats and today I want to begin another related topic that of hibernation. I say it"s related because animals that hibernate must find a location in their habitat to care for themselves during the period of inactivity. Hibernation is just that—a state of inactivity. To understand hibernation and the animals that hibernate, you need to be familiar with the definition of a few words. A dictionary entry defines "hibernate" as "to pass the winter in a torpid or resting state". "Torpid" means losing power or a state of sluggishness and the word "torpor" means "extreme sluggishness".
In addition to the resting state when there is hibernation, there is also a metabolic depression which means that the animal"s metabolism has slowed down considerably and that the rate of metabolism has dropped.
So, when you have an animal in hibernation you will find that the animal"s rate of metabolism is lower, the animal has slower breathing, and the animal has a lower body temperature. I am sure that all of you think of the bear when you are asked to give an example of an animal that hibernates. But bears are not the only animals that hibernate. Bats and groundhogs do, too. Snakes go through a similar process but it is not called hibernation. Usually birds are not thought to hibernate. But there is one bird, the poor-will, that does hibernate.
As you read more about hibernation you will learn that the terms "torpor" and "torpid" are used in connection with the concept of hibernation but there are some differences. So for the purpose of this lecture, understand that hibernation and torpor involve a sluggishness of the body and slowed body functions throughout a time period usually winter.
If you think back to the books you read as a child, you will probably remember stories about bears eating up huge amounts of food before they went into a cave to sleep away the winter. You will probably also remember that the bears were enormous in size before they went into the cave and that they were thin and extremely hungry when they awoke in the spring and re-entered the world.
What happens is that when the bears eat this enormous amount of food, they store fat, or energy, in their bodies to survive the period of hibernation. There is not as much food to metabolize during hibernation, so the metabolic rate slows considerably. Also, their hearts beat more slowly and they consume less oxygen. Although bears" body temperatures are lowered during hibernation, the temperatures are usually only lowered about ten or fifteen degrees. That is different from some mammals whose body temperatures are lowered drastically almost to the point of freezing. Why do I tell you this? Well, the significance is that mammals whose body temperature doesn"t drop as much can be more easily disturbed during the winter and awakened by extreme noise. When that happens the bear can abandon its site of hibernation and can die if unable to find a food supply. Since bear cubs are born during hibernation, if a mother bear would abandon her den during the time she is nursing the cubs, the cubs could potentially have a life threatening situation.
You might find it interesting that a female bear can hibernate longer than a male and bears riving ha more northern climates will hibernate longer than bears living farther south.
Student A: You mentioned that bats hibernate. Do they hibernate in caves like the bears?
Professor: Yes, often they do. Bats also store up food during the summer for their winter months of hibernation.
Student A: Are there any differences between a bear"s hibernation and a bat"s?
Professor: Yes. Bats often stay in caves during the winter but they often stay in groups. Now there can be a single bat that isn"t interested in group living during the winter, but most are. And they hang upside down to hibernate. I suppose that might be a very big difference between bats and bears. Also, the length of time of hibernation will be different. As I indicated, a bear may hibernate several months, in fact some have hibernated up to eight months. That"s two-thirds of a year! Bats may hibernate in old buildings or the hollows of trees. A bear might hibernate in the hollow of a tree but, of course, a bear could probably not get away with hibernating in an old building!
Student A: Probably one reason is that there would be too much space in an old building.
Professor: Yes, that"s right. Bears like to curl up but the problem is that usually their dens are very small, not having any extra room, and the openings to their dens are just large enough to squeeze through.
Student B: Don"t bats curl up, too, when they hibernate?
Professor: Yes, they do. Even when they hang upside down from a ceiling of a cave or building, they curl up in a ball.

[解析] 教授在讲座的刚开始就说明了讲座的主要内容：We have been talking about animals" habitats and today I want to begin another related topic that of hibernation. D选项的描述最为准确。