问题 单项选择题

TCP和UDP提供了“端口号”,其作用是______。

A.标明特定主机的标识

B.标明特定的应用实体

C.便于路由选择时能提高算法效率

D.指明本主机只能为一个进程提供服务

答案

参考答案:B

解析: 传输层对应的传输用户是应用进程,或称应用实体。通常,传输层会对应多个应用进程,即一个主机上有多个进程并行运行,如在多任务或多用户多任务系统中。TCP和UDP提供了“端口号”了来区分这些进程。TCP和UDP都预留了一些重要的端口号,如TCP中HTTP的端口号为80,FTP的端口号为21等。

阅读理解

In the days when an ice cream sundae cost much less, a 10-year-old boy entered a hotel coffee shop and sat at a table. A waitress put a glass of water in front of him. “How much is an ice cream sundae?” “Fifty cents,” replied the waitress. The little boy pulled his hand out of his pocket and studied a number of coins in it. “How much is a dish of plain ice cream?” he required. Some people were now waiting for a table and the waitress was a bit impatient. “Thirty-five cents,” she said rudely. The little boy again counted the coins. “I’ll have the plain ice cream,” he said. The waitress brought the ice cream, put the bill on the table and walked away. The boy finished the ice cream, paid the bill and departed. When the waitress  came back, she began wiping down the table and then swallowed hard at what she saw. There, placed nearly beside the empty dish, were two five-cent coins and five one-cent coins---her tip.

1. In the days , an ice cream is ______________.

A. dearer than usual                B. as dear as usual

C. much cheaper than usual          D. as cheap as usual

2.How much money did the boy probably have in his pocket?

A. thirty-five cents.      B. More than fifty cents. 

C. only fifty cents.       D. Less than fifty cents.

3.Why did the little boy have only a dish of plain ice cream?

A.The plain ice cream cost him much less.

B.He enjoyed the cheaper ice cream better.

C.The coins were not enough for an ice cream sundae.

D.  He wanted to save some coins to tip the waitress.

4.We can infer that the waitress might have felt _____ when she got the tip.

A. very surprised.                B. a bit of shame

C. quite pleased                  D. a little worried

填空题