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对路由选择协议的一个要求是必须能够快速收敛，所谓“路由收敛”是指（）
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OSPF协议使用（）分组来保持与其邻居的连接
A lot of kids are getting online these days- sharing date, talking about social issues, meeting adults as well as kids, and learning about other cultures. There seems to be everything on the network. Just like any other form of media, the quality of this massive collection of information isunequal, and there is good information as well as rubbish. Networks hold great promise;however, they are also home to people who mean to hurt others or use their technical knowledgeto steal from them. Although many Web pages can teach kids useful things, there are some othersites waiting to tempt young people who are immature and easily affected.By now, you may shake your head, but wait, let's try to put the problem into perspective.Generally, it's safe for kids to use the Internet. The number of sites considered harmful isbetween 1% and 3%，which shows about 4.5 million other sites are interesting and educational.Besides, to stop children from using these services just because crimes are being comitted onlinewould be like telling them not to attend college because students may have accidents on campus.What can parents do to protect their children from those harmful sites? The simplest solutionis the use of programs which block offensive sites. Such programs are set to screen out certainwords likely to appear on“unhealthy" sites. But many sites inappropriate to young people areclever at using words with double meanings that may appear harmless. What's more, not only dothe programs fail to do the job satisfactorily, they also take away the decisive role of parents inchildren's education. A child who downloads bad information or pictures can only be corrected bypositive family influence. No filtering program is necessary for a child who has learned to say“no”to sites he knows are inappropriate for him.Today, when children are exposed to technology at a younger age, parents often findthemselves lagging behind in computer skills. Surprisingly, this may be the key to yourinvolvement. What is a better way to learn about the Internet than to do so alongside yourchildren? They'll most likely pick it up more quickly than you do, of course, but youll have thechance to see, and take pride in, your child at work. You may search for information thatinterets your child together with him and get to know the“friends”he has online, just as youwould get to know his other friends.Thoughful parents would combine supervision with communication, which is the best way totake advantage of the Internet as a resource while proteting their children. Follow their examplesand have fun with kids on the Net!51. According to the passage, is it wisc for parents to keep their children away from thecomputer? Why?A) No. Because there are also millions of sites which are interesting and educational.B) No. Because their children have the right to use the computer.C Yes. Because there are many rubbish sites which may hurt children.D) Yes. Because children may become addicted to computer games.52. In the last two paragraphs, parents are advised to__________.A) learn about the Internet along with their childrenB) watch their children while they are at workC) search for information for their childrenD) make friends with their children53. According to the article, the best way to protect children as well as take advantage of theInternet is__________.A) the use of filering programsB) parents' mastery of computer skillsC) the combination of supervision and communicationD) forbidding them to make friends on the Internet54. Which of the following is closest in meaning to the underlined expression“lagging behind"?A) hiding behindB) running behindC) walking behindD) falling behind
将物理信道的总频带宽分割成若干个子信道，每个子信道传输一路信号，这是（ ）。
双绞线由两个具有绝缘保护层的铜导线互相绞在一起组成，这样可以（ ）
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