VPN（Virtual Private Network,虚拟专用网络)连接是跨互联网建立的一条临时的安全的连接,是一条穿越不安全公共网络的可靠的隧道。（)

A.CCC(Circuit Cross Connect)

B.SVC(Switched Virtual Channel)

C.Martini信令方式的PWE3(Pseudo-Wire Emulation Edge to Edge)

D.PWE3异种介质互联

ectangle 的直接派生类和Shape 的间接派生类。请模仿Rectangle 类，写出Circle 类的所有成员函数。

/****************** 文件shape.h*************************/

const float PI=3.14159f; // 定义圆周率常量

class Shape // 几何图形抽象类

{

public:

virtual float GetPerimeter()=0; // 纯虚函数，计算周长

virtual float GetAre()=0; // 纯虚函数，计算面积

};

class Rectangle: public Shape // 矩形类

{

public:

Rectangle (float len,float wid):length(len),width(wid){}

~Rectangle (){}

float GetPerimeter() {return 2*(length width);} // 计算矩形周长

float GetAre() {return length*width;} // 计算矩形面积

private:

float length, width; // 矩形的长和宽

};

class Circle: public Shape // 圆类

{

public: // 在下面编写每个成员函数

private:

float rad; // 圆的半径

};

class Square: public Rectangle // 正方形类

{

public:

Square(float len): Rectangle(len,len){}

~Square(){}

};

tap the consumer market. More recently, as the Web proved to be more than a fashion, companies have started to buy and sell products and services with one another. Such business-to-business sales make sense because business people typically know what product they're looking for.

Nonetheless, many companies still hesitate to use the Web because of doubts about its reliability. "Businesses need to feel they can trust the pathway between them and the supplier," says senior analyst Blanc Erwin of Forrester Research. Some companies are limiting the risk by conducting online transactions only with established business partners who are given access to the company's private intranet.

Another major shift in the model for Internet commerce concerns the technology available for marketing. Until recently, Internet marketing activities have focused on strategies to "pull" customers into sites. In the past year, however, software companies have developed tools that allow companies to "push" information directly out to consumers, transmitting marketing messages directly to targeted customers. Most notably, the Pointcast Network uses a screen saver to deliver a continually updated stream of news and advertisements to subscribers' computer monitors. Subscribers can customize the information they want to receive and proceed directly to a company's Web site. Companies such as Virtual Vineyards are already starting to use similar technologies to push messages to customers about special sales, product offering, or other events. But push technology has earned the contempt of many Web users. Online culture thinks highly of the notion that the information flowing onto the screen comes there by specific request. Once commer-cial promotion begins to fill the screen uninvited, the distinction between the Web and television fades. That's a prospect that horrifies Net purists.

But it is hardly inevitable that companies on the Web will need to resort to push strategies to make money. The examples of Virtual Vineyards, Amazon.com, and other pioneers show that a Web site selling the right kind of products with the right mix of interactivity, hospitality, and security will attract online customers. And the cost of computing power continues to free fall, which is a good sign for any enterprise setting up shop in silicon. People looking back 5 or 10 years from now may well wonder why so few companies took the online plunge.

What do we learn about the present web business？

A．Web business is no longer in fashion.

B．Business-to-business sales are the trend.

C．Web business is prosperous in the consumer market.

D．Many companies still lack confidence in web business.

A.VMware

B.Virtual Judge

C.Virtual Box

D.Virtual PC

A.suddenly

B.usually

C.seldom

A.Very reliable forwarding

B.Virtual routing forwarding instances

C.Vip redundancy features

D.Virtual routing format

A．Less virtual communication and less time with family.

B．Shallower relationship and less comparison of lives.

C．Less face to face communication and fewer friends indeed.

D．Less actual conversation and less satisfaction with lives.