GRE历年题目解析
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14-7-27 10:15 PM第一：我用的这套gre历年真题是陈琦团队整理的，如有不妥，请告知我，随时撤下。
第二：按照这套真题的顺序，由简入难，从最简单的level 1开始，我将努力分析每篇阅读，并及时发上来，但是其中有些文章肯定会有分析错误，所以请大家帮我提出来，大家一起讨论，这才是我发这个贴的主要目的。
第三：分析当中涉及一些概念:TW主题词，TS主题句，KW论点，a\b\c\d\e\f\g….都为说明性内容或者论据。
1.The molecules of carbon dioxide1The molecules of carbon dioxide in the Earth’s atmosphere affect the heat balance of the Earth by acting as a one-way screen. 2 Although these molecules allow radiation at visible wavelengths, where most of the energy of sunlight is concentrated, to pass through, they absorb some of the longer-wavelength, infrared emissions radiated from the Earth’s surface, radiation that would otherwise be transmitted back into space. 3 For the Earth to maintain a constant average temperature, such emissions from the planet must balance incoming solar radiation. 4 If there were no carbon dioxide in the atmosphere, heat would escape from the Earth much more easily.5 The surface temperature would be so much lower that the oceans might be a solid mass of ice.1 Today, however, the potential problem is too much carbon dioxide.2 The burning of fossil fuels and the clearing of forests have increased atmospheric carbon dioxide by about 15 percent in the last hundred years, and we continue to add carbon dioxide to the atmosphere.3 Could the increase in carbon dioxide cause a global rise in average temperature, and could such a rise have serious consequences for human society?4 Mathematical models that allow us to calculate the rise in temperature as a function of the increaseindicate that the answer is probably yes.1 Under present conditions a temperature of-18℃ can be observed at an altitude of 5 to 6 kilometers above the Earth.2 Below this altitude (called the radiating level), the temperature increases by about 6℃ per kilometer approaching the Earth’s surface, where the average temperature is about 15℃.3 An increase in the amount of carbon dioxide means that there are more molecules of carbon dioxide to absorb infrared radiation.4 As the capacity of the atmosphere to absorb infrared radiation increases, the radiating level and the temperature of the surface must rise.1 One mathematical model predicts that doubling the atmospheric carbon dioxide would raise the global mean surface temperature by 2.5℃.2 This model assumes that the atmosphere’s relative humidity remains constant and the temperature decreases with altitude at a rate of 6.5℃ per kilometer.3 The assumption of constant relative humidity is important, because water vapor in the atmosphere is another efficient absorber of radiation at infrared wavelengths.4 Because warm air can hold more moisture than cool air, the relative humidity will be constant only if the amount of water vapor in the atmosphere increases as the temperature rises.5 Therefore, more infrared radiation would be absorbed and reradiated back to the Earth’s surface.6 The resultant warming at the surface could be expected to melt snow and ice, reducing the Earth’s reflectivity.7 More solar radiation would then be absorbed, leading to a further increase in temperature.第一段：1句：TW 提出本文的主题词（carbon dioxide），提出carbon dioxide可以影响地球的热平衡，预测下文将详细介绍原理，如何影响。
2句：说明性内容a，详细介绍平衡原理，carbon dioxide放过太阳光，吸收一部分由地面反射的辐射和热量，这里正好体现了首句里的one-way screen。
3句：说明性内容b，介绍平衡原理，由太空射入和由地面反射的辐射要平衡，也就是吸收和释放的要平衡。
4句：说明性内容c，介绍平衡原理，carbon dioxide的作用就是防止地球反射的热量全部跑掉。
5句：说明性内容d，介绍平衡原理，没有carbon dioxide地球温度将非常低。
（这句话对于论证基本没有什么实质性作用，我认为是废话一句）第二段：1句：提出问题，KW （problem is too much carbon dioxide）;第一段讲的是背景信息，carbon dioxide的重要性，第二段开始由however转折，提出carbon dioxide过多的问题。
预测下文将详细介绍具体的问题。
2句：说明性内容a：具体介绍carbon dioxide为何越来越多，相当背景信息，但并没有讲carbon dioxide带来的具体问题是什么，后文保持对具体问题的期待。
(我认为这句话也没有什么实际意义，没有直接回应首句的观点。
)3句：KW’：通过提问的方式引出论点（包括两个方面，一、carbon dioxide过多是否导致温度升高；二、温度升高是否会给人类带来坏处。
），通过本段首句，我们知道答案是肯定的。
4句：KW’:重现首句观点，carbon dioxide太多是个问题(简单说就是carbon dioxide会导致global rise in temperature、也会导致serious consequences)，预测后文将介绍具体的原理，如何发生的。
第三段：1句：KW的论据a1：在离地面5-6公里的高度，温度为-18℃。
2句：KW的论据a2：高度每降低1公里，温度升高6℃；地表平均温度为15℃。
3句：KW的论据a3：carbon dioxide增加导致吸收更多的辐射。
4句：KW的论据a4：辐射增多导致rise of temperature。
这段回答了第一个问题，即是carbon dioxide增多是否会导致温度升高，但温度升高不一定就会有不好的影响，因此预测下文会论述第二个问题，即carbon dioxide导致温度的升高是否会进一步对人类社会带来不好的影响。
另外，本段1、2句为3、4句的论述提供了事实与前提，事实就是随着高度降低，温度升高，前提就是随着高度降低，carbon dioxide的含量在增加，不过总的来看，这四句话为并列关系。
第四段：(与第三段平行关系，都是KW的论据)1句：本段论点KW1：研究提出carbon dioxide增加2倍，地表温度升高2.5摄氏度。
预测后文将介绍具体机制原理。
2句：论据b1：该模型假设大气平均湿度不变，并且从地表往上高度每增加1公里，温度降低6.5摄氏度。
3句：论据b2：大气中的水蒸气也可以吸收辐射。
4句：论据b3：只有当温度升高时，水气也随之升高，相对湿度才会保持不变。
