正确答案: A

细胞内高K+浓度和安静时膜主要对K+有通透性

题目：大多数细胞产生和维持静息电位的主要原因是 （　　）

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学习资料的答案和解析：

[单选题]回答{TSE}题Never laugh at a snow covered mountain! Laughter and yelling, during the avalanche season, can cause a deadly pile of snow．Huge snow slides are most common in mountains where there are steep slopes that are well buried in snow and ice．The snow builds up slowly and lands very softly．This can create a very touchy, unstable situation．Tons of snow may be held up by only the friction between snowflakes．The deep snow is like a house of cards．The slightest movement can cause it to fall．As soon as something slips, this great mass of snow will come crashing down the mountainside．Slides may be started by sound vibrations．They may also be started by the weight of wet, melting snow．Once an avalanche has been triggered, the cause no longer matters．Moving down a steep slope, it picks up great speed and added snow．Some avalanches travel as fast as two hundred miles per hour．The force of an avalanche will mow down anything in its path．Whole houses have been swallowed up by these fast-paced piles of snow．The wind that is caused by an avalanche is almost as destructive as the snow itself．Winds from an avalanche have been known to travel as fast as those of a tornado．So, when approaching a thickly snow covered mountain, speak softly!{TS}Avalanches can be started by________

loud sounds

解析：【原文大意】永远也不要在大雪覆盖的山上大笑!在雪崩的季节，大笑和大喊都会引起惨重的雪崩。在山上被雪和冰覆盖的陡坡最容易产生大块雪的滑动。雪慢慢地集中起来，轻轻地落下，造成非常敏感且不稳定的态势。数吨的雪可能仅靠雪花之间的摩擦支撑。深深的雪如同纸牌搭的房子，最轻微的活动都会使它倒塌。一旦有东西滑动，巨大的雪块就会冲下山坡。声波会引起滑动，湿的、溶化的雪的重量也可能引起滑动。一旦雪崩产生，其产生的原因就不再重要了。雪崩冲下陡坡，速度在加快，卷入更多的雪。有些雪崩的速度相当于每小时200英里的速度。它的力量可以摧毁沿途的一切。整个的房子被这些急速的雪堆吞噬。由雪崩引起的风几乎同雪崩自身一样是毁灭性的。这些风的速度可与飓风匹敌。因此，当靠近大雪覆盖的大山时，轻声说话!第二段。下雪本身并不能引起雪崩。最后一段说雪崩可引起风，而不是风引起雪崩。雪花之间的摩擦说明积雪不牢固。只有选项c是正确的。

[单选题]We can conclude from this passage that avalanches________

回答下面的题目Never laugh at a snow covered mountain! Laughter and yelling, during the avalanche season, can cause a deadly pile of snow．Huge snow slides are most common in mountains where there are steep slopes that are well buried in snow and ice．The snow builds up slowly and lands very softly．This can create a very touchy, unstable situation．Tons of snow may be held up by only the friction between snowflakes．The deep snow is like a house of cards．The slightest movement can cause it to fall．As soon as something slips, this great mass of snow will come crashing down the mountainside．Slides may be started by sound vibrations．They may also be started by the weight of wet, melting snow．Once an avalanche has been triggered, the cause no longer matters．Moving down a steep slope, it picks up great speed and added snow．Some avalanches travel as fast as two hundred miles per hour．The force of an avalanche will mow down anything in its path．Whole houses have been swallowed up by these fast-paced piles of snow．The wind that is caused by an avalanche is almost as destructive as the snow itself．Winds from an avalanche have been known to travel as fast as those of a tornado．So, when approaching a thickly snow covered mountain, speak softly!Avalanches can be started by________

have killed people

解析：选项A和B在文中并未提及。文中提到雪崩的强大力量，可以毁掉整座房子，人肯定也是有伤亡的。选项C是正确的。

[单选题]_________

根据以下内容，回答下面的题目。Insure means to protect _51_ a loss of money．Most people can budget their money so that their income will cover expected expenses _52_ food, clothing, housing, and public services．But, there is no way to know _53_ who will suffer a crisis (危机) such as a serious illness, fire, flood, or a car accident．Such crises usually _54_ great expense．Even if people could predict crises, it would be hard to save enough money to _55_ the expenses．Insurance is a system _56_ a company collects money from many individuals and then pays certain expenses whenever one of those insured individuals is faced with a certain crisis．An insurance policy _57_ how much the insurance costs and how much the company will pay when a policy holder is faced with a certain crisis．There are many different kinds of insurance, _58_ hospital, motor-car and fire．Insurance can be rather expensive but most people buy insurance of some kinD．Insurance is something _59_ people buy and hope they will _60_ need．_________

take

[单选题]“Would you be_________do it for me，please?”“Of course，with pleasure．”

SO kind as to

[单选题]Sequoyah was a young Cherokee Indian．son of a white trader and an Indian Squaw(北美印第安女人)．At an early age，he became fascinated by“tile talking leaf”，an expression thathe used to describe the white man’s written records．Although many believe this"talking leaf”to be a gift from tile Great Spirit，Sequoyah refused to accept that theory．Like other Indians oftile period，he was illiterate，but his determination to remedy tile situation led to the inventionof a unique 86 character alphabet based on the sound patterns that he heard． 　　His family and friends thought him mad，but while recuperating(恢复)from a huntingaccident．he diligently and independently set out to create a form of communication for his ownpeople as well as for other Indians．In l821，after twelve years of work，he had successfully de。veloped a written language that would enable thousands of Indians to read and write． 　　Sequoyah’s desire to preserve words and events for later generation has caused him to be remembered among the important inventors．The giant redwood trees of-California，called“se-quoias(红杉)”in his honor，will further imprint his name in history． 根据以上内容，回答{TSE}题。{TS}What is the most important reason that Sequoyah wiU be remeIll]bered?

He created a unique alphabet．

[单选题]EverythingDepends on__________we get a raise in our salary．

whether

[单选题]How will the government know what the air quality is?

根据下列短文，回答下面的题目。　　A panel of government officials is worried．The air quality in some areas is not good．Theair is polluted with soot．The officials worry that the air is harmful to the people who breathethe air．The officials are expels．They study the environment．They diSCUSS ways to stop theair pollution．The panel decided to make，some changes to the law．　　The mew plan places strict limits on how much soot call be released into the air．Now，ameasurement of 65 parts of soot is considered safe．The new plan would reduce that number to30．The daily limit of pollution in the air would be cut in half．　　These new standards would affect industry．The limits would also affect people who ownwood stoves and fireplaces．The country will keep track of the air quality every day．Peoplewould be required to stop burning wood when the levels are high．They could also install a kindof special fireplace．These fireplaces burn very little wood．They do not pollute the air asmuch．Some countries will punish families who violate the ban．They will have to pay a fine fornot complying with the law．　　Some states do not have much industry．Their pollution problem is not too bad．Theywould stiU have to regulate how much pollution is released into the air．The experts hope thatthis ban will help keep the air cleaner．Before the plan becomes a law the public will have a chance to comment on it．Citizenswill have ninety days to ask questions and voice concerns about the plan．Then it will becomea law．The panel is made up of________．

Scientists will test it every day．

[多选题]下列关于良性肿瘤特点的叙述，正确的是（　　）

呈膨胀性扩展

肿瘤边界清楚

细胞形态变异较小