按传输模式分类,光纤可以分为()和多模光纤两类。

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问题:

按传输模式分类,光纤可以分为()和多模光纤两类。

考点:线路运行与检修专业考试线路运行与检修专业考试题库
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In the early days of the internet, the idea that it represented an entirely new and separate realm, distinct from the real world, was seized upon by both advocates and critics of the new technology. Advocates liked the idea that the virtual world was a placeless datasphere, liberated from constraints and restrictions of the real world, and an opportunity for a fresh start. For instance, John Perry Barlow, an internet activist, issued the "Declaration of the Independence of Cyberspace" in February 1996. He thundered, "Governments of the industrial world, I come from cyberspace, the new home of mind. Cyberspace does not lie within your borders. We are creating a world that all may enter without privilege or prejudice accorded by race, economic power, military force, or station of birth."

Where Mr. Barlow and other cyber-Utopians found the separation between the real and virtual worlds exciting, however, critics regarded it as a cause for concern. They worried that people were spending too much time online, communicating with people they had never even met in person in chat rooms, virtual game worlds and, more recently, on social-networking sites such as MySpace and Facebook. A study carried out by the Stanford Institute for the Quantitative Study of Society in 2000, for example, found that heavy internet users spent less time talking to friends and family, and warned that the internet could be "the ultimate isolating technology".

Both groups were wrong, of course. The internet has not turned out to be a thing apart. Unpleasant aspects of the real world, such as taxes, censorship, crime and fraud are now features of the virtual world, too. Garners who make real money selling swords, gold and other items in virtual game worlds may now find that the tax man wants to know about it. Designers of virtual objects in Second Life, an online virtual world, are resorting to real-world lawsuits in order to protect their intellectual property.

At the same time, however, some of the most exciting uses of the internet rely on coupling it with the real world. Social networking allows people to stay in touch with their friends online, and plan social activities in the real world. The distinction between online and offline chatter ceases to matter. Or consider Google Earth, which puts satellite images of the whole world on your desktop and allows users to link online data with specific physical locations.

All these approaches treat the internet as an extension or an attachment to the physical world, not a separate space. Rather than seeing the real and virtual realms as distinct and conflicting, in short, it makes sense to see them as complementary and connected. The resulting fusion is not what the Utopians or the critics foresaw, but it suits the rest of us just fine.

From the passage we can find that the author()

A. supports both advocates and critics of the internet

B. believes that the real and virtual worlds are interdependent

C. is opposed to the fusion of the internet with the physical world

D. argues that real and virtual worlds are distinct and conflicting

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两个相似三角形最长边分别为10cm和25cm,它们的周长之差为60cm,则这两个三角形的周长分别是                 

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液相在烧结过程中的主要作用是什么?

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英语作文。
     过生日互赠礼物在中学生中似乎成为一种时尚,甚至有的学生还去饭店搞生日聚会。对此,
同学们有不同的看法。假设你是王平,请你根据下表提示,给某英语报社的编辑写一封信,
并谈谈自己的观点。
赞成为同学们提供交际机会;利于增进同学之间的友谊;学习之余可以放松心情。
反对容易造成对时间和金钱的浪费;导致攀比;对青少年学习和成长造成不利影响。
你的观点 ......
注意:1. 词数:120--150左右 (信的开头和结尾已经给出,但不计入总词数。) 
          2. 短文须包括表中的全部内容,可以适当增加细节,以使行文连贯。           
          3. 参考词汇:攀比:keep up with the Joneses
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能够实现“收回用户U4对学生表(STUD)中学号(XH)的修改权”的SQL语句是______。

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