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问题 填空题

一个长方形长a米，宽b米．如果将它的长增加3米，它的面积增加______平方米．

答案

（a+3）×b-ab，

=ab+3b-ab，

=3b（平方米）；

答：它的面积增加3b平方米；

故答案为：3b．

问答题

如图所示电路，电源电压保持不变，闭合开关S，当变阻器滑片P在中点a处时，电流表读数为0.6 A；当滑片P在b端时，电压表读数为5 V，电流表读数为0.5 A，请根据测得的数据计算出前后两次在电阻R1上消耗的功率．
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单项选择题


TEXT A
Video conferencing is gradually becoming an accepted means in which to do business. For a long time is suffered from the image of the video conferencing suite, cumbersome and expensive to operate with long booking lead times. Its use tended to be confined to special executive meetings on different continents and its practicality for everyday uses tended to be overlooked. That was perfectly understandable given the state of the technology. But desktop video conferencing entered the market with an explosion of publicity several years ago and has been growing at a steady rate since. Market predictions show growth rates of around 60-100% year on year as more and more companies axe beginning to embrace the concepts and applications of video conferencing.
Changes in the way we work are going to provide one of the most important spurs to the growth in the use of this technology. Mobile working is making traditional communications methods obsolete and rapid information exchange a priority. Video conferencing is well positioned to help companies who have a heavy reliance on immediate employee communications to meet this need in the ever-changing working environment.
For those who are new to video conferencing it is worth defining the key areas of video conferencing to help in understanding the market. Video conferencing enables audio and video transmission between separate locations from anywhere in the world. Video conferences can be point-to-point exactly like a telephone call, or multi-point enabling virtual meetings amongst three or more locations to take place, both most commonly using an ISDN network.
Multi-point conferences require a physical device called a Multi-point Contro Unit (MCU) or "bridge". The MCU’s function is to recognize that each participant is using an industry standard and then connect all the participants together. The technical complexities of operating a bridge requires a telecom department within a organization. However most choose to avoid the costs and work associated with this and use a multi-point service provider which is where AT&T expertise lies.
Intel who produce the Proshare desktop conferencing software were actively targeting the business markets and trying to drive down the cost of video conferencing, they believe video conferencing will be "the norm" in the future and as common as any other software currently residing on your PC.
The main advantage of the desktop product is the data sharing capability, which allows a user to hunch a software application and share it with other users. The power of this is clear to sec. Documents can be agreed and amended with desktop users throughout the world in real-time, instead of faxing documents backwards and forwards with comments or trying to make changes over the phone which often leads to mistakes being made. In a multi-point environment application sharing operates using the T. 120 industry standard.
Your PC is always available to you on your desk and all you need to do to set up a meeting with three or mote people is to reserve a call with a multi-point service provider such as AT＆T and dial into a bridge. You can then be linked with up to 24 different worldwide locations. Not only will you save time and money, you will also develop more effective face to face working relationships with your colleagues, customers or suppliers.

From the passage, we can safely infer that ______.

A．the use of video conferencing is still a mystery for the general public

B．video conferencing may be as simple as telephones for communication

C．face to face relationship is important for customers and suppliers

D．video conferencing is especially popular with information technology firms
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