问题 单项选择题

在采用点一点通信信道的通信子网中,如果两个结点之间没有连接的线路,那么它们之间的通信只能通过中间结点_______。

A.广播

B.转接

C.接收

D.协议变换

答案

参考答案:B

解析:[知识点] 计算机网络的定义与分类[评析] 在广播式网络中,所有连网计算机共享一个公共通信信道。当一台计算机利用共享通信信道发送报文分组时,所有其他的计算机都会“收听”到这个分组。由于发送的分组中带有目的地址和源地址,接收到该分组的计算机将检查目的地址是否与本结点地址相同。如果被接收报文分组的目的地址与本结点地址相同,则接收该分组,否则丢弃该分组。 与广播式网络相反,在点一点网络中,每条物理线路连接一对计算机。假如两台计算机之间没有直接连接的线路,那么它们之间的分组就要通过中间结点的接收,存储、转发,直至目的结点。由于连接多台计算机之间的线路结构可能是复杂的,因此从源结点到目的结点可能存在多条路由,决定分组从通信子网的源结点到达目的结点的路由需要有路由选择算法。采用分组存储转发与路由选择是点一点式网络与广播式网络的重要区别之一。

阅读理解

阅读理解。

     EDGEWOOD-Every morning at Dixie Heights High School, customers pour into a special experiment:

the district's first coffee shop run mostly by students with special learning needs.

     Well before classes start, students and teachers order Lattes, Cappuccinos and Hot Chocolates. Then,

during the first period, teachers call in orders on their room phones, and students make deliveries.

     By closing time at 9.20 a.m., the shop usually sells 90 drinks.

     "Whoever made the chi tea, Ms. Schatzman says it was good," Christy McKinley, a second year student,

announced recently, after hanging up with the teacher.

     The shop is called the Dixie PIT, which stands for Power in Transition. Although some of the students

are not disabled, many are, and the PIT helps them prepare for life after high school.

     They learn not only how to run a coffee shop but also how to deal with their affairs. They keep a timecard

and receive paychecks, which they keep in check registers.

     Special-education teachers Kim Chevalier and Sue Casey introduced the Dixie PIT from a similar program

at Kennesaw Mountain High School in Georgia. 

     Not that it was easy. Chevalier's first problem to overcome was product-related. Should schools be selling

coffee? What about sugar content?

     Kenton County Food Service Director Ginger Gray helped. She made sure all the drinks, which use non-fat

milk, fell within nutrition (营养) guidelines.

     The whole school has joined in to help.

     Teachers agreed to give up their lounge (休息室) in the mornings. Art students painted the name of the shop

on the wall. Business students designed the paychecks. The basketball team helped pay for cups.

1. What is the text mainly about? [ ]

A. A best-selling coffee.

B. A special educational program.

C. Government support for schools.

D. A new type of teacher-student relationship.

2. The Dixie PIT program was introduced in order to _____. [ ]

A. raise money for school affairs

B. do some research on nutrition

C. develop students' practical skills

D. supply teachers with drinks

3. How did Christy McKinley know Ms. Schatzman's opinion of the chi tea? [ ]

A. She met her in the shop.

B. She heard her telling others.

C. She talked to her on the phone.

D. She went to her office to deliver the tea.

4. We know from the text that Ginger Gray _____. [ ]

A. manages the Dixie P1T program in Kenton County

B. sees that the drinks meet health standards

C. teaches at Dixie Heights High School

D. owns the school's coffee shop

单项选择题