第一篇文章indus文明的衰落

　　第一部分讲一个古文明(印加)的衰落。 这个文明的衰落不是因为战争;也不是因为某一群人的定居，因为那群人是在衰落之后才到哪个地方去的。

　　第二部分讲overgrazing和deforestation 可能是原因。 因为人们到哪使用fireplace以及一些其他的自然资源。

　　第三部分另一个原因可能是降雨量。科学家发现，那个地方衰落的时候正好是降雨量减少的时候。还具体描述了在这段时期降雨量发生的变化，给出很多数据。

　　第四部分另一个原因是城市的繁荣跟周边rural地区食物的productivity有关。由于气候的原因，rural地区食物产量降低，大城市不能从周围地区获得食物就衰落了。同时，小地方没大城市衰落那么快，但最后变成了village。整个文明也就衰落了

　　解析：该篇文章为因果解释类文章，先描述现象印加文明的衰落然后解释不同的原因。典型的托福阅读cause-effect类文章。大家按照不同的理论整理文章结构即可。具体内容请大家参照如下文章。

　　Decline Of Harappan Civilization:

　　The Indus Valley Civilization dated from 3300 1300 BCE that was located in the north western region of the Indian Subcontinent. Flourishing around the Indus River basin, the civilization primarily centered along the Indus and the Punjabregion, extending into the Ghaggar-Hakra River valley and the Ganges-Yamuna Doab, encompassing most of what is now Pakistan, the western states of modern-day India, as well as extending into southeastern Afghanistan, and the eastern most part of Balochistan, Iran. The mature phase of this civilization is known as the Harappan Civilization, as the first of its cities to be unearthed was the one at Harappa, excavated in the1920s in what was at the time the Punjab province of British India (now in Pakistan).

　　The decline of Harappan culture is difficult to explain. During its late phase between 2000 and 1700 BC 'The Indus Valley Civilization as a distinct entity gradually ceased to exist'. Historians have different opinions regarding the causes of the decay and disappearance of the Harappan culture. Various causes have been ascribed for its weakening and then decay: Increase in rainfall, earthquake, decrease in fertility of soil, floods, Aryan invasion, disease etc. Mortimer Wheeler pointed out that the Harappan culture was destroyed by the Aryans. The Aryans were more skilled at warfare and were powerful than the Harappans. But there is very little evidence on this opinion.

　　.Another school of thought relates the demise of the Indus valley civilization to have been brought about by a major tectonic shift that caused continuous floods of this area. Research has proved that the decline of the glorious Harappan culture was due to a variety of factors, both manmade and natural.

　　In the beginning of the second millennium BC, there were great changes in the environmental conditions-the climate changed and large parts of the plains were flooded when tectonic changes threw up a dam in the lower Indus Valley. There were also other socio-economic factors that contributed to the decline. Agricultural production declined with the changes in the climate and the big cities could no longer sustain themselves. People from the major centers perhaps left for the smaller outposts and slowly riveted back to village life when they could no longer maintain the prerequisites of an urban existence. The causes of its decline are not certain. However, the physical existence of the civilization ended due to various factors: Economical changes led to the decline of land and agriculture, thereby enforcing the need to evacuate to other area might have been the reason for the disintegration of the Indus Valley. Shifts in the monsoon pattern and changes in temperature led to the areas more arid. Increase in Population, excessive deforestation, decline in agriculture etc. might have created economic problems leading to the gradual decay of the culture. The marked decline in the quality of building and town planning indicates that the authorities were losing control. The changes in the river flow pattern and correspondent widespread flooding would have disrupted the agricultural base.?

　　第二篇文章 大陆板块漂移理论

　　航海发现化石相似性得出G原来是一个大陆。之后提出可能是由land bridge联系起来的。但是这个原因不足以解释这个现象。

　　之后提出了板块漂移理论。中间举了许多例子来证明这个理论的正确性。包括动植物化石的相似性，以及大陆板块边缘的吻合，一些现在分离的地区有非常相似的地址特征。

　　这个理论一开始不被接受，直到1960年由于研究地球磁场得出新的证据，该理论才被其他理论支持。引出了魏格纳以及另一位科学家提出的Plate tectonic theory。

　　解析：本篇文章重点为论述大陆板块漂移理论对动植物相似性的解释，文章中存在大量论证关系。考生按照不同的证据对于板块漂移理论的支持即可整理文章的结构。具体内容请大家参照如下文章。

　　Wegener and his predecessors

　　The hypothesis that the continents had once formed a single landmass before breaking apart and drifting to their present locations was first presented by Alfred Wegener to the German Geological Society on 6 January 1912.Although Wegener's theory was formed independently and was more complete than those of his predecessors, Wegener later credited a number of past authors with similar ideas: Franklin Coxworthy (between 1848 and 1890), Roberto Mantovani (between 1889 and 1909), William Henry Pickering (1907) and Frank Bursley Taylor (1908).

　　Evidence that continents 'drift'

　　Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around different continent shores, suggesting that they were once joined. The fossils of Mesosaurus, a freshwater reptile rather like a small crocodile, found both in Brazil and South Africa, are one example; another is the discovery of fossils of the land reptile Lystrosaurus from rocks of the same age from locations in South America, Africa, and Antarctica. There is also living evidence—the same animals being found on two continents. Some earthworm families (e.g.: Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa, for instance.

　　The complementary arrangement of the facing sides of South America and Africa is obvious, but is a temporary coincidence. In millions of years, slab pull and ridge-push, and other forces of tectonophysics will further separate and rotate those two continents. It was this temporary feature which inspired Wegener to study what he defined as continental drift, although he did not live to see his hypothesis become generally accepted.

　　Widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites, suggested the existence of the supercontinent of Gondwana, which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, in modern coordinates, and supported the idea that the southern continents had previously been in dramatically different locations, as well as contiguous with each other.

　　Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around different continent shores, suggesting that they were once joined. The fossils of Mesosaurus, a freshwater reptile rather like a small crocodile, found both in Brazil and South Africa, are one example; another is the discovery of fossils of the land reptile Lystrosaurus from rocks of the same age from locations in South America, Africa, and Antarctica.There is also living evidence—the same animals being found on two continents. Some earthworm families (e.g.: Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa, for instance.

　　The complementary arrangement of the facing sides of South America and Africa is obvious, but is a temporary coincidence. In millions of years, slab pull and ridge-push, and other forces of tectonophysics will further separate and rotate those two continents. It was this temporary feature which inspired Wegener to study what he defined as continental drift, although he did not live to see his hypothesis become generally accepted.

　　Widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites, suggested the existence of the supercontinent of Gondwana, which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, in modern coordinates, and supported the idea that the southern continents had previously been in dramatically different locations, as well as contiguous with each other.

　　第三篇文章 pest control

　　文章第一部分化学手段进行防治。但是化学手段存在缺点：但是由于害虫的繁殖速度快， 同时农药还大量杀死的predator, 但是predator 就没这么幸运了，他们不能大量繁殖，而且毒素可以传递到他们身体里，从而杀死prdator，这一点造成了害虫数量的增加。举了中国的例子，作为第一个采用化学防治的例子。

　　文章第二部分将采用天敌进行防治。引进的pest的天敌也许会成功，但是最后predator一段时间之后也可能成为另一种危害。举了california的例子说明。

　　文章第三步部分说明在用上述方法综合使用。首先先考虑化学方法，如果不能控制就引入天敌，但是只要能够控制在不造成经济危害的基础之上.

　　解析;文章重点为探讨两种对于害虫的控制方法，生物控制和化学控制，分别探讨各自的优缺点。最后提出二者的综合，提出操作的过程。大家按照不同方法的不同特点梳理文章的重点信息即可。

　　Chemical Control

　　Chemical pesticides are substances that are manufactured in laboratories that, when applied to crops, reduce the vitality of pest populations while leaving crops unharmed. There are many chemicals available to help eradicate common pests in a number of ways. Chemical controls can kill pests that come in contact with the chemical (toxicants), eliminate the reproductive potential of pests (sterilants), disrupt their developmental potential (growth regulators) or influence their behavior (semiochemicals). Most of these chemical controls are fast acting and effective.

　　Biological Control

　　Biological control methods employ the use of living organisms such as predators, parasites and pathogens to control the populations of pests on agricultural crops. Biological control agents can be bred and reared in large numbers and then released into infected crops to reduce the populations of pests (augmentation) or simple land conservation measures can be implemented on agricultural lands that maintain healthy populations of native predators (conservation). Many pests that cause damages to crops thrive because they are invasive and have no natural predators. Finding and importing predators of these invasive pests is essential for effective biological pest control.

　　Benefits

　　Chemical controls are cheap and readily available. Chemical controls, especially toxicants, have been in use since the 1940's and have remained in popular use due to their fast acting and effective results in controlling pest populations. Many new chemicals have been developed in recent years that are even more efficient in controlling pests, maintaining the popularity of chemical control in agricultural practices. However, biological control has seen an increase in use in recent years due to its perennial and organic nature. Many biological control methods remain in effect year after year, limiting pests without any additional costs or synthetic additives to the natural environment.

　　Considerations

　　While chemical controls are often effective they are usually seasonal and require reapplication with each growing season. Biological controls may take a longer period of time to see the desired results, but they only require the initial investment and introduction to control pests. Chemical controls also have additional environmental costs. Many chemical pesticides are persistent in the environment, damage organisms other than the pests they are meant to control (including humans) and are not permanently effective, as pest populations can build up a resistance to chemicals over time. Thus, while chemical controls may be more economical and effective in the short term, their use requires caution and consideration for future costs, both environmental and economic.

　　Integration

　　While some landowners look only at seasonal profits and depend on chemical methods, others contemplate only the environmental sustainability of their practices and opt for biological methods. However, many landowners blend chemical and biological controls together in order to maximize profits while minimizing costs as well as reduce the environmental impact on their land. The use of multiple pest control methods is referred to as integrated pest management (IPM). Dense infestations often require the potency of chemical pest control but limited application, coupled with preventative biological control, is the most effective agricultural management practice.