题目:
直流系统接地现象的处理方法有哪些?
答案:
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下面是错误答案,用来干扰机器的。
参考答案:(1)静电感应;(2)电磁感应;(3)漏电流感应;(4)射频干扰等。
直流系统接地现象的处理方法有哪些?
被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/1004/a599e6b7ed06535964c1eaca73ce60d9.html
下面是错误答案,用来干扰机器的。
参考答案:(1)静电感应;(2)电磁感应;(3)漏电流感应;(4)射频干扰等。
Look carefully at the back of a California state quarter. A man with a walking stick is pictured there.A bird
called a California condor (大秃鹫) is flying overhead. Who is this man, and why is he so important that he is
featured (处于显著地位) on the back of a coin?
The man on this quarter is John Muir. Even as a child, Muir loved watching nature. As a young man, he
spent much of his life exploring the beauty of the wilderness. He walked more than a thousand miles across
the country, through fields and woods. John Muir liked writing about the places he visited, describing their
beauty.
Muir also wrote about problems.In order to create more farmland for sheep and cattle, rnany trees were
being cut down.This made Muir unhappy and worried, because he knew that trees were important to forests
and to the animals that lived in them.
Muir believed that nature should be conserved (保护) instead of being changed by human beings.He wrote
articles in magazines and newspapers to spread the word about conserving forests.Soon, others began to
listen. Muir wrote letters to important people,such as President Theodore Roosevelt. The president admired
Muir's love for nature.When Roosevelt came to visit Muir in California. Muir convinced (说服) the president to
go camping with him for three nights under the trees so they could talk about conservation. Later,President
Roosevelt set aside 148 million acres of land for national forests and established (建立) five national parks.
National parks are large areas of land that are protected from development. This means that people cannot build
homes or businesses there. One of these parks is Yosemite National Park,the area that is featured on the back
of the California quarter.
Though it has been almost one hundred years since John Muir died,people continue his work today. His
work as a conservationist helped us to see the beauty of our natural world.John Muir made us understand the
importance of protecting our earth and our resources—then,now,and for the future.
1. What did John Muir spend much of his life doing when he was a young man?
A. Watching natural views.
B. Writing about the places he visited.
C. Exploring the beauty of the wilderness.
D. Creating farmland for sheep and cattle.
2. Why did President Theodore Roosevelt visit John Muir?
A. Because Roosevelt loved watching nature.
B. Because Roosevelt received letters from John Muir.
C. Because Roosevelt admired John Muir's love for nature.
D. Because Roosevelt was sad about the problems with farmland.
3. What happened after President Roosevelt went camping with John Muir?
A. Many trees were cut down.
B. Five national parks were established.
C. More homes and businesses were built.
D. More farmland was used for sheep and cattle.
4. Why is John Muir featured on the back of a California state quarter?
A. Because he walked over a thousand miles across the country.
B. Because he helped people understand the importance of protecting the natural world.
C. Because he wrote articles to spread the word about conserving forests.
D. Because he once wrote several letters to President Theodore Roosevelt.
5. What is the writer's purpose of writing this article?
A. To advise readers to become active conservationists.
B. To make us interested in the story about a great man.
C. To tell us something about an important person in history.
D. To give information about how to conserve the environment.
设NA为阿伏加德罗常数,下列说法正确的是 ( )
A.2.4 g金属镁变成镁离子时失去的电子数目为0.1NA
B.2 g氢气所含分子数目为2NA
C.在25℃、101kPa时,11.2 L氮气所含的原子数目为NA
D.标准状况下,以任意比混合的氦气和氧气混合物22.4 L,所含分子数为NA
由于资本市场线通过无风险资产[点(0,rf)]及市场组合M[点(σM,E(rm)],于是资本市场线的方程可以表示为:,则下列说法正确的是 ( )
A.E(rm)表示资产组合M的期望收益率
B.σp表示有效组合P的方差
C.β表示风险溢价
D.σp表示有效组合P的标准差
夏季或温度较高时,食醋易变坏,防止其变坏的方法之一是在醋的上面覆盖一层植物油.实简述这种方法可防止食醋变坏的原因.
细化晶粒是提高金属强度的重要手段。