5.　　　 A system frequently used in decentralized organizations in which computing power is located and shared at different sites is _________

A.　　 client / server

B.　　　 centralized

C.　　　 mainframe

D.　　 distributed

专题六　 科学技术练习答案及详解

Passage 51　　 1. C　　 2. D

科学和我们日常生活紧密相连。

4.　　　 Rules for exchanging data on a network are called _______.

A.　　 protocol

B.　　　 asynchronous transmission

C.　　　 configuration

D.　　 serial transmission

3.　　　 What communications channel transfers data as pulses of light? ______

A.　　 Telephone lines

B.　　　 Coaxial cable

C.　　　 Fiber-optic cable

D.　　 Microwave

2.　　　 Transferring data from a larger computer to your microcomputer is called

A.　　 a LAN

B.　　　 time-sharing

C.　　　 downloading

D.　　 uploading

1.　　　 A special sequence of numbers or letters that limits access to electronic boxes is a ____________

A.　　 combination

B.　　　 code

C.　　　 password

D.　　 modem

4.According to the passage, which is NOT true about “I love you” virus?

A.　　 Have found who made it

B.　　　 Have found the solution to it

C.　　　 Have been attacked by it

D.　　 Have no effective method to

Passage 60　　 Application proxy

To understand the application proxy, consider this scenario where you needed to deliver your neat little package of network data. With application-level proxies, the scenario is similar, but now you need to rely on someone else to deliver the package for you. Hence the term proxy illustrates this new scenario. The same rules apply as they do for packet filtering, except that you don’t get to deliver your package past the gate. Someone will do it for you, but that agent needs to look inside the package first to confirm its contents. If the agent has permission to deliver the contents of the package for you, he will.

Most commercial routers do not have proxy capabilities today, although I believe that proxy technology will be integrated with router code in the future. Until then, you need to rely on a standalone system that can support application-level proxy services.

Since an application proxy needs to communicate on behalf of the sender, it needs to understand the specific language or protocols associated with a particular application. Take as an example the widely used HTTP (Hypertext Transfer Protocol) proxy. If you are using a browser on your network, it is highly likely that your IS group has an HTTP proxy configured to allow you to access the Web via a central server. That single machine understands HTTP conversations and can speak on behalf of the requesting client. This is application level proxying.

Of course, security and encryption also come into play, since the proxy must be able to open the “package” to look at it or decode its contents. These are important issues obviously, but to do them justice would require another article.

3.All the following countries have been attacked by “I Love You” Virus EXCEPT __________

A.　　 Britain

B.　　　 Australia

C.　　　 Switzerland

D.　　 Japan

2.The most terrible character “I Love You” Virus is _______

A. it can hide in computers for long

B. it can damage computer’s normal programs

C. it can get rid of all the information that the operator stores

D .it can reproduce itself in great quantities in a short time

1. In 1999, the virus made American scientists’ information ________

A.　　 all lost

B.　　　 partly lost

C.　　　 none lost

D.　　 mostly lost

5.According to the passage, what should be given to cloning’s inventors? _____________

A.　　 Strict control

B.　　　 Great thanks

C.　　　 Care

D.　　 Caution

Passage 59　 “I love you” virus

On May 21, 1999, some American scientists were working at the computers to look for information they needed. Suddenly they saw a lot of very bright red spots crossing the computers’ screens. At the same time the computers were working much slower. To find out what was happening they stopped their work to check some parts of the computers. To their horror, they found out that most of their stored information was got rid of by computer virus! Obviously all these computers had been infected by computer virus.

It is said that the computer virus was made by two or three Philippine young men fond of playing tricks. They all had excellent education. They created the virus just to show their intelligence. The kind of computer virus is named “I Love You” Virus. This virus can hide in computers for long. When the time comes it will attack the computers by lowering the important functions, damaging their normal programs or even getting rid of a great deal of information which operators of the computers often use or store; even worse, it still can reproduce itself in great quantities within a short time.

We come to know that “I Love You” Virus often attacks computers on Mondays and that it is spreading to many computers in the world. Among the countries that suffered computer viruses last year are Britain, Australia, Switzerland and the US. Those who made the computer viruses have been found out slowly and carefully. But till now, how to get rid of the terrible viruses remains a problem.