问题 单项选择题

某企业单位局域内中,客户机通过代理服务器访问Internet的连接方式如图1-4所示。IP地址为 192.168.1.100的客户机配置“TCP/IP网络属性”时,其中“默认网关”的设置内容应是 (68) 。该客户机访问Internet中p地址为220.110.10.222的Web站点时,经由代理服务器后数据包的源IP地址为 (69)


答案

参考答案:C

解析:[要点解析] 在连入Internet时,所有客户机都要申请一个IP地址,但IP地址的划分已不能满足用户对连入Internet的需求,而使用代理服务器是解决这一矛盾的方法之一。首先将单位内部需要接入Internet的计算机连成一个局域网,然后通过代理服务器连入Internet,这样就可以使多台计算机共用一个Internet上的IP地址,即共用一个出口连入Internet,从而减少用户单位申请IP地址的费用。通常,代理服务器上安装有两块网卡,其中一块接内部局域网,另一块接外部网络,此时代理服务器可以起到一个边界路由器的作用。因此,地址为192.168.1.100的客户机网卡配置“TCP/IP网络属性”时,其中“网关”的设置为192.168.0.1。
网络地址转换(NAT,Network Address Translation)是Internet工程任务组标准,允许一个整体机构以一个公网IP地址出现在Internet上,即把内部私有IP地址(常用的地址范围为10.0.0.0~10.255.255.255、 172.16.0.0~172.31.255.255、192.168.0.0~192.168.255.255)翻译成公网合法IP地址。可见,NAT就是在局域网内部网络中使用内部地址,而当内部结点要与外部网络进行通信时,就在网关处,将内部IP地址替换成公网IP地址,从而使内网主机能够正常访问Internet。
NAT功能通常被集成到路由器、防火墙、ISDN路由器或者单独的NAT设备中。网络管理员只需在这些网络安全设备中设置NAT功能,就可以实现对内部网络的屏蔽。对于本试题,IP地址为192.168.1.100的客户机访问Internet时,经由代理服务器后,由NAT技术进行源地址的转换,转换后数据包的源地址为代理服务器外口的地址,即220.110.10.1。

阅读理解

Sugar—free beets(甜菜)that still taste sweet, tastier tomatoes and brighter-colored fruits and vegetables that stay ripe(熟的)longer are all foods that are being grown now. How can they

carry traits, such as being tastier, brighter, and riper? They are genetically engineered.

Genetic engineering(基因工程)is like making a change in a recipe. For example, when you make cakes, you mix together all of the usual ingredients. If you add an extra ingredient, like salt, the cakes will taste differently.

Genes are ingredients in the recipe for life. They carry the traits of living things. Your genes dictate what color hair and eyes you’ll have, how tall you’ll be, as well as many other traits. Genes carry traits for plants, too. By adding genes to a plant, you can sometimes create new traits. For example, adding a certain gene to a potato plant can make the potato plant distasteful to bugs(虫子). This makes some farmers happy because they don’t have to use chemicals to keep bugs away from their plants.

It sounds great, but some people are opposed to the idea of food that is genetically engineered. Ronnie Cummins, from the Campaign for Food Safety, is against it. He says that one of the major concerns is allergies(过敏). Supermarkets don’t always label foods that are genetically engineered. A customer could unknowingly buy food that has an added gene from another plant that he or she is allergic to. It could be dangerous.

Gary Burton from Monsanto, a seed(种子)company that engineers food, disagrees. He says his company tests for allergies. Burton believes that genetic engineering is a valuable tool for making better food. The technology can help farmers use less insecticide(杀虫剂)and grow healthier crops. Burton thinks there are many advantages.

But Cummins says that we just don’t know what will happen in the future if we keep adding genes to foods. We could mistakenly create a monster.

People have different opinions about genetic engineering. One side supports it and thinks it will only help us. The other side is opposed to playing with nature and fears health risks. Which side do you think is right?

小题1:What could be a good thing about food that is genetically engineered?

A.It’s more expensive.

B.It could taste different.

C.It requires less insecticide.

D.It’s not labeled in the supermarket.小题2:In general, who does not support the idea of genetic food?

A.People from seed companies.

B.Farmers who use engineered seeds.

C.People from the Campaign for Food Safety.

D.Scientists who create genetically engineered food.小题3:It can be inferred that          .

A.growing genetic foods will make farmers richer

B.people will eat more genetic foods in the future

C.using fewer chemicals could make the food tastier

D.there could be unknown dangers about genetic foods小题4:What is the best title of this passage?

A.Future Farming

B.Genetic Engineering

C.Foods with a Difference

D.Genetically Engineered Fruits

填空题