【单选题】【消耗次数：1】
计算机网络有局域网和广域网之分,其划分依据是( )。
①
通信传输的介质
②
网络拓朴结构
③
信号频带的占用方式
④
通信的距离
参考答案：
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相关题目
【多选题】
计算机网络拓朴结构有论述正确的有：（ ）。
①
网络拓朴不涉及信号的流动，只关心介质的物理连接形态
②
网状结构是局域网中主要的拓朴结构之一
③
星型拓朴中故障的定位容易
④
环型结构中对网络的扩展比较困难
随机题目
【单选题】
阅读理解：阅读下列短文，回答文后问题，选择最佳答案Trees mainly serve man in three important ways: They provide him with wood and other products; they provide him shade; and they help to prevent droughts and floods.Unfortunately, in many parts of the world, man has not realized that the third of these services is the most important．In his eagerness to make money from trees, he has cut them down in large numbers, only to find that without them he has lost the best friends he had. And besides, he is usually too careless to plant and look after new trees. So the forests slowly disappear.This does not only mean that man will have fewer trees. The results are even more serious: for where there are trees, their roots break up soil allowing the rain to sink in and also bind(固定) the soil, thus preventing it from being washed away easily；but where there are no trees, the rain falls on hard ground and flows away, causing floods and carrying away the rich top-soil. When the top-soil is gone, nothing remains but worthless desert.Two thousand years ago，a rich and powerful country cut down its trees to build warships, with which to gain itself an empire．It set up the empire, but, without its trees, its soil became poor and grew weak. When the empire fell to pieces, the home country found itself faced by floods and starvation(饥荒)．3. Land becomes desert after all trees are cut down because __________.
①
A. roots of trees break up the soil
②
B. no tree keeps the rain and protects the top-soil
③
C. strong winds bring a lot of sand
④
D. there are too many rainfalls to make it
【单选题】
阅读理解：阅读下列短文，回答文后问题，选择最佳答案Trees mainly serve man in three important ways: They provide him with wood and other products; they provide him shade; and they help to prevent droughts and floods.Unfortunately, in many parts of the world, man has not realized that the third of these services is the most important．In his eagerness to make money from trees, he has cut them down in large numbers, only to find that without them he has lost the best friends he had. And besides, he is usually too careless to plant and look after new trees. So the forests slowly disappear.This does not only mean that man will have fewer trees. The results are even more serious: for where there are trees, their roots break up soil allowing the rain to sink in and also bind(固定) the soil, thus preventing it from being washed away easily；but where there are no trees, the rain falls on hard ground and flows away, causing floods and carrying away the rich top-soil. When the top-soil is gone, nothing remains but worthless desert.Two thousand years ago，a rich and powerful country cut down its trees to build warships, with which to gain itself an empire．It set up the empire, but, without its trees, its soil became poor and grew weak. When the empire fell to pieces, the home country found itself faced by floods and starvation(饥荒)．1. According to the passage, which is the most important service of trees to man?
①
A. They help him make money.
②
B. They give him cool.
③
C. They give him wood and other things.
④
D. They help him to stop droughts and floods.
【单选题】
These papers___yet.
①
have not written
②
have not been written
③
has not written
④
has not been written