【单选题】【消耗次数:1】
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).Which title best fits the passage?
Trees and Man
The Function of Tree Wood
How do People do with Trees?
The Usage of Tree Roots
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【单选题】 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).Land becomes desert after all trees are cut down because __________.
①  roots of trees break up the soil
②  no tree keeps the rain and protects the top-soil
③  strong winds bring a lot of sand
④  there are too many rainfalls to make it
【单选题】 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).In many places forests slowly disappear because __________.
①  many trees have been cut down by man
②  new trees are not well looked after
③  man has not paid enough attention to planting trees
④  all the above
【单选题】 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).Why did the country mentioned in the passage suffer from floods and starvations?
①  Because it set up an empire.
②  Because it fell to pieces.
③  Because it turned its trees into warships.
④  Because it spent too much money on wars.
【单选题】 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).According to the passage, which is the most important service of trees to man?
①  They help him make money.
②  They give him cool.
③  They give him wood and other things.
④  They help him to stop droughts and floods.
【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).5. Which title best fits the passage?
①  A. Trees and Man
②  B. The Function of Tree Wood
③  C. How do People do with Trees?
④  D. The Usage of Tree Roots
【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).2. In many places forests slowly disappear because __________.
①  A. many trees have been cut down by man
②  B. new trees are not well looked after
③  C. man has not paid enough attention to planting trees
④  D. all the above
【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】 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).4. Why did the country mentioned in the passage suffer from floods and starvations?
①  A. Because it set up an empire.
②  B. Because it fell to pieces.
③  C. Because it turned its trees into warships.
④  D. Because it spent too much money on wars.
【单选题】 He lives in a village _____there are a lot of trees.
①  there
②  where
③  that
④  which
随机题目
【单选题】 关于单相桥式PWM逆变电路,下面说法正确的是( )
①  在一个周期内单极性调制时有一个电平,双极性有两个电平
②  在一个周期内单极性调制时有两个电平,双极性有三个电平
③  在一个周期内单极性调制时有三个电平,双极性有两个电平
④  在一个周期内单极性调制时有两个电平,双极性有一个电平
【单选题】 如某晶闸管的正向阻断重复峰值电压为 745V,反向重复峰值电压为 825V,则该晶闸管的额定电压应为( )
①  700V
②  750V
③  800V
④  850V
【单选题】 电阻性负载三相半波可控整流电路中,控制角的范围是( )
①  30°~150°
②  0°~120°
③  15°~125°
④  0°~150°
【单选题】 单相半控桥电感性负载电路中,在负载两端并联一个续流二极管的作用是( )
①  增加晶闸管的导电能力
②  抑制温漂
③  增加输出电压的稳定性
④  防止失控现象的产生
【单选题】 PWM脉宽调制型逆变电路中,采用不可控整流电源供电,也能正常工作。
①  A
②  B
【判断题】 若增大 SPWM 逆变器的输出电压基波频率,可采用的控制方法是增大正弦调制波频率。(      )
①  正确
②  错误
【判断题】 关于单相桥式 PWM逆变电路在一个周期内单极性调制时有三个电平,双极性有两个电平。(      )
①  正确
②  错误
【判断题】 晶闸管稳定导通的条件是晶闸管阳极电流小于晶闸管的擎住电流。(      )
①  正确
②  错误
【判断题】 三相半波可控整流电路的自然换相点是。(      )
①  正确
②  错误
【判断题】 在晶闸管触发电路中,若使控制电压 UC=0,改变交流相电压的过零点的大小,可使直流电动机负载电压 Ud=0,使触发角α=90o。达到调定移相控制范围,实现整流、逆变的控制要求。(      )
①  正确
②  错误