问题 单项选择题

在 ISO/OSI 参考模型中,网络层的主要功能是______。

A.组织两个会话进程之间的通信,并管理数据的交换

B.数据格式变换、数据加密与解密、数据压缩与恢复

C.路由选择、拥塞控制与网络互连

D.确定进程之间通信的性质,以满足用户的需要

答案

参考答案:C

解析:网络层的功能是在信源和信宿之间建立逻辑链路,为报文或报文分组的传递选择合适的路由以实现网络互联。为进行路由选择,要选择合适的路由选择算法,并针对网络情况实现拥塞控制。

单项选择题
阅读理解

阅读理解。

     How could we possibly think that keeping animals in cages in unnatural environments-mostly for

entertainment purposes-is fair and respectful? Zoo officials say they are concerned about animals. However,

most zoos remain "collection" of interesting "things" rather than protective habitats (栖息地).

     Zoos teach people that it is acceptable to keep animals bored, lonely, and far from their natural homes.

     Zoos claim to educate people and save endangered species, but visitors leave zoos without having leamed

anything meaningful about the animals' natural behavior, intelligence, or beauty. Zoos keep animals in small

spaces or cages, and most signs only mention the species' name, diet, and natural range.

     The animals' normal behavior is seldom noticed because zoos don't usually take care of the animals' natural

needs. The animals are kept together in small spaces, with no privacy and little opportunity for mental and

physical exercise. This results in unusual and self-destructive behavior called zoochosis. A world-wide study

of zoos found that zoochosis is common among animals kept in small spaces or cages. Another study showed

that elephants spend 22 percent of their time making repeated head movements or biting cage bars, and bears

spend 30 percent of their time walking back and forth, a sign of unhappiness and pain.

     Furthermore, most animals in zoos are not endangered. Captive breeding (圈养繁殖) of endangered big

cats, Asian elephants, and other species has not resulted in their being sent back to the wild. Zoos talk a lot

about their captive breeding programs because they do not want people to worry about a species (物种) dying

out. In fact, baby animals also attract a lot of paying customers. Haven't we seen enough competitions to name

baby animals?

     Actually, we will save endangered species only if we save their habitats and put an end to the reasons people

kill them. Instead of supporting zoos, we should support groups that work to protect animals' natural habitats.

1. How would the author describe the animals' life in zoos?[ ]

A. Dangerous.

B. Unhappy.

C. Natural.

D. Simple.

2. In the state of zoochosis, animals ____ according to the passage. [ ]

A. remain in cages

B. behave strangely

C. often attack other animals

D. enjoy walking around

3. What does the author try to argue in the passage? [ ]

A. Zoos are not worth the public support.

B. Zoos fail in their attempt to save animals.

C. Zoos should treat animals as human beings.

D. Zoos use animals as a means of entertainment.

4. The author tries to persuade readers to accept his argument mainly by ____. [ ]

A. pointing out the faults in what zoos do

B. giving examples of animals in the wild

C. questioning the way animals live

D. discussing the advantages of natural habitats

5. Although he is against zoos, the author would still admit that ____. [ ]

A. zoos have to keep animals in small cages

B. most animals in zoos are endangered species

C. some endangered animals are reproduced in zoos

D. it's acceptable to keep animals away from their habitats