雅思阅读真题题源五篇

　　雅思阅读真题题源第一篇：蚂蚁智力

　　Collective intelligence:：Ants and brains neurons

　　STANFORD - An individual ant is not very bright, but ants in a colony, operating as a collective, do remarkable things.

　　A single neuron in the human brain can respond only to what the neurons connected to it are doing, but all of them together can be Immanuel Kant.

　　That resemblance is why Deborah M. Gordon, StanfordUniversity assistant professor of biological sciences, studies ants.

　　39;m interested in the kind of system where simple units together do behave in complicated ways, she said.

　　No one gives orders in an ant colony, yet each ant decides what to do next.

　　For instance, an ant may have several job descriptions. When the colony discovers a new source of food, an ant doing housekeeping duty may suddenly become a forager. Or if the colonys territory size expands or contracts, patroller ants change the shape of their reconnaissance pattern to conform to the new realities. Since no one is in charge of an ant colony - including the misnamed queen, which is simply a breeder - how does each ant decide what to do?

　　This kind of undirected behavior is not unique to ants, Gordon said. How do birds flying in a flock know when to make a collective right turn? All anchovies and other schooling fish seem to turn in unison, yet no one fish is the leader.

　　Gordon studies harvester ants in Arizona and, both in the field and in her lab, the so-called Argentine ants that are ubiquitous to coastal California.

　　Argentine ants came to Louisiana in a sugar shipment in 1908. They were driven out of the Gulf states by the fire ant and invaded California, where they have displaced most of the native ant species. One of the things Gordon is studying is how they did so. No one has ever seen an ant war involving the Argentine species and the native species, so its not clear whether they are quietly aggressive or just find ways of taking over food resources and territory.

　　The Argentine ants in her lab also are being studied to help her understand how they change behavior as the size of the space they are exploring varies.

　　The ants are good at finding new places to live in and good at finding food, Gordon said. Were interested in finding out how they do it.

　　Her ants are confined by Plexiglas walls and a nasty glue-like substance along the tops of the boards that keeps the ants inside. She moves the walls in and out to change the arena and videotapes the ants movements. A computer tracks each ant from its image on the tape and reads its position so she has a diagram of the ants activities.

　　The motions of the ants confirm the existence of a collective.

　　A colony is analogous to a brain where there are lots of neurons, each of which can only do something very simple, but together the whole brain can think. None of the neurons can think ant, but the brain can think ant, though nothing in the brain told that neuron to think ant.

　　For instance, ants scout for food in a precise pattern. What happens when that pattern no longer fits the circumstances, such as when Gordon moves the walls?

　　Ants communicate by chemicals, she said. Thats how they mostly perceive the world; they dont see very well. They use their antennae to smell. So to smell something, they have to get very close to it.

　　The best possible way for ants to find everything - if you think of the colony as an individual that is trying to do this - is to have an ant everywhere all the time, because if it doesnt happen close to an ant, theyre not going to know about it. Of course, there are not enough ants in the colony to do that, so somehow the ants have to move around in a pattern that allows them to cover space efficiently.

　　Keeping in mind that no one is in charge of a colony and that there is no central plan, how do the ants adjust their reconnaissance if their territory expands or shrinks?

　　No ant told them, OK, guys, if the arena is 20 by 20. . . . Somehow there has to be some rule that individual ants use in deciding to change the shape of their paths so they cover the areas effectively. I think that that rule is the rate in which they bump into each other.

　　The more crowded they are, the more often each ant will bump into another ant. If the area of their territory is expanded, the frequency of contact decreases. Perhaps, Gordon thinks, each ant has a threshold for normality and adjusts its path shape depending on how often the number of encounters exceeds or falls short of that threshold.

　　If the territory shrinks, the number of contacts increases and the ant alters its search pattern. If it expands, contact decreases and it alters the pattern a different way.

　　In the Arizona harvester ants, Gordon studies tasks besides patrolling. Each ant has a job.

　　I divide the tasks into four: foraging, nest maintenance, midden and patrolling - patrollers are the ones that come out first in the morning and look for food. The foragers go where the patrollers find food.

　　The colony has about eight different foraging paths. Every day it uses several of them. The patrollers go out first on the trails and they attract each other when they find food. By the end of an hours patrolling, most patrollers are on just a few trails. . . . All the foragers have to do is go where there are the most patrollers.

　　Each ant has its prescribed task, but the ants can switch tasks if the collective needs it. An ant on housekeeping duty will decide to forage. No one told it to do so and Gordon and other entomologists dont know how that happens.

　　No ant can possibly know how much food everybody is collecting, how many foragers are needed, she said. An ant has to have very simple rules that tell it, OK, switch and start foraging. But an ant cant assess globally how much food the colony needs.

　　39;ve done perturbation experiments in which I marked ants according to what task theyre doing on a given day. The ants that were foraging for food were green, those that were cleaning the nest were blue and so on. Then I created some new situation in the environment; for example, I create a mess that the nest maintenance workers have to clean up or Ill put out extra food that attracts more foragers.

　　It turns out that ants that were marked doing a certain task one day switch to do a different task when conditions change.

　　Of about 8,000 species of ants, only about 10 percent have been studied thus far.

　　Its hard to generalize anything about the behavior of ants, Gordon said. Most of what we know about ants is true of a very, very small number of species compared to the number of species out there.

　　雅思阅读真题题源第二篇：天才儿童

　　TIME: 5-7

　　HOW IQ BECOMES IQ

　　In 1904 the French minister of education, facing limited resources for schooling, sought a way to separate the unable from the merely lazy. Alfred Binet got the job of devising selection principles and his brilliant solution put a stamp on the study of intelligence and was the forerunner of intelligence tests still used today. He developed a thirty-problem test in 1905, which tapped several abilities related to intellect, such as judgment and reasoning. The test determined a given childs mental age. The test previously established a norm for children of a given physical age. For example, five-year-olds on average get ten items correct, therefore, a child with a mental age of five should score 10, which would mean that he or she was functioning pretty much as others of that age. The childs mental age was then compared to his physical age.

　　A large disparity in the wrong direction might suggest inability rather than laziness and means that he or she was earmarked for special schooling. Binet, however, denied that the test was measuring intelligence and said that its purpose was simply diagnostic, for selection only. This message was however lost and caused many problems and misunderstandings later.

　　Although Binets test was popular, it was a bit inconvenient to deal with a variety of physical and mental ages. So, in 1912, Wilhelm Stern suggested simplifying this by reducing the two to a single number. He divided the mental age by the physical age and multiplied the result by 100. An average child, irrespective of age, would score 100. a number much lower than 100 would suggest the need for help and one much higher would suggest a child well ahead of his peer.

　　This measurement is what is now termed the IQ score and it has evolved to be used to show how a person, adult or child, performed in relation to others. The term IQ was coined by Lewis m. Terman, professor of psychology and education of Stanford University, in 1916. He had constructed an enormously influential revision of Binets test, called the Stanford-Binet test, versions of which are still given extensively.

　　The field studying intelligence and developing tests eventually coalesced into a sub-field of psychology called psychometrics . The practical side of psychometrics became widespread quite early, by 1917, when Einstein published his grand theory of relativity, mass-scale testing was already in use.

　　Germanys unrestricted submarine warfare provoked the United States to finally enter the first world war in the same year. The military had to build up an army very quickly and it had two million inductees to sort out. Who would become officers and who enlisted men? Psychometricians developed two intelligence tests that helped sort all these people out, at least to some extent. This was the first major use of testing to decide who lived and who died since officers were a lot safer on the battlefield. The tests themselves were given under horrendously bad conditions and the examiners seemed to lack common sense. A lot of recruits simply had no idea what to do and in several sessions most inductees scored zero! The examiners also came up with the quite astounding conclusion from the testing that the average American adults intelligence was equal to that of a thirteen-year-old!

　　Nevertheless, the ability for various authorities to classify people on scientifically justifiable premises was too convenient and significant to be dismissed lightly, so with all good astounding intentions and often over enthusiasm, societys affinity for psychological testing proliferated.

　　Back in Europe, Sir Cyril Burt, professor of psychology at University College London from 1931 to 1950, was a prominent figure for his contribution to the field. He was a firm advocate of intelligence testing and his ideas fitted in well with English cultural ideas of elitism. A government committee in 1943 used some of Burts ideas in devising a rather primitive typology on childrens intellectual behavior. All were tested at age eleven and the top 15 or 20 per cent went to grammar schools with good teachers and a fast pace of work to prepare for the few university places available. A lot of very bright working-class children, who otherwise would never have succeeded, made it to grammar schools and universities.

　　The system for the rest was however disastrous. These children attended lesser secondary or technical schools and faced the prospect of eventual education oblivion. They felt like dumb failures, which having been officially and scientifically branded. No wonder their motivation to study plummeted. It was not until 1974 that the public education system was finally reformed. Nowadays it is believed that Burt has fabricated a lot of his data. Having an obsession that intelligence is largely genetic, he apparently made up twin studies, which supported this idea, at the same time inventing two co-workers who were supposed to have gathered the results.

　　Intelligence testing enforced political and social prejudice and their results were used to argue that Jews ought to be kept out of the United States because they were so intelligently inferior that they would pollute the racial mix. And blacks ought not to be allowed to breed at all. Abuse and test bias controversies continued to plaque psychometrics.

　　Measurement is fundamental to science and technology. Science often advances in leaps and bounds when measurement devices improve. Psychometrics has long tried to develop ways to gauge psychological qualities such as intelligence and more specific abilities, anxiety, extroversion, emotional stability, compatibility with marriage partner and so on. Their scores are often given enormous weight. A single IQ measurement can take on a life of its own if teachers and parents see it as definitive. It became a major issue in the 70s when court cases were launched to stop anyone from making important decisions based on IQ test scores. the main criticism was and still is that current tests dont really measure intelligence. Whether intelligence can be measured at all is still controversial. some say it cannot while others say that IQ tests are psychologys greatest accomplishments.

　　雅思阅读真题题源第三篇：全球变暖

　　A Canary in the Coal Mine

　　The Arctic seems to be getting warmer. So what?

　　A. Climate change in the Arctic is a reality now! So insists Robert Corell, an oceanographer with the American Meteorological Society. Wild-eyed proclamations are all too common when it comes to global warming, but in this case his assertion seems well founded.

　　B. At first sight, the ACIAs reports conclusions are not so surprising. After all, scientists have long suspected that several factors lead to greater temperature swings at the poles than elsewhere on the planet. One is albedo the posh scientific name for how much sunlight is absorbed by a planets surface, and how much is reflected. Most of the Polar Regions are covered in snow and ice, which are much more reflective than soil or ocean. If that snow melts, the exposure of dark earth acts as a feedback loop that accelerates warming. A second factor that makes the poles special is that the atmosphere is thinner there than at the equator, and so less energy is required to warm it up. A third factor is that less solar energy is lost in evaporation at the frigid poles than in the steamy tropics.

　　C. And yet the language of this weeks report is still eye-catching: the Arctic is now experiencing some of the most rapid and severe climate change on Earth. The last authoritative assessment of the topic was done by the UNs Intergovernmental Panel on Climate Change in 2001. That report made headlines by predicting a rise in sea level of between 10cm and 90cm, and a temperature rise of between 1.4C and 5.8C over this century. However, its authors did not feel confident in predicting either rapid polar warming or the speedy demise of the Greenland ice sheet. Pointing to evidence gathered since the IPCC report, this weeks report suggests trouble lies ahead.

　　D. The ACIA reckons that in recent decades average temperatures have increased almost twice as fast in the Arctic as they have in the rest of the world. Skeptics argue that there are places, such as the high latitudes of the Greenland ice sheet and some buoys at sea, where temperatures seem to have fallen. On the other hand, there are also places, such as parts of Alaska, where they have risen far faster than average. Robin Bell, a geophysicist at Columbia University who was not involved in the reports compilation, believes that such conflicting local trends point to the value of the international, interdisciplinary approach of this weeks report. As he observes, climate change, like the weather, can be patchy and you can get fooled unless you look at the whole picture.

　　E. And there is other evidence of warming to bolster the ACIAs case. For example, the report documents the widespread melting of glaciers and of sea ice, a trend already making life miserable for the polar bears and seals that depend on that ice. It also notes a shortening of the snow season. The most worrying finding, however, is the evidence still preliminary that the Greenland ice sheet may be melting faster than previously thought.

　　F. That points to one reason the world should pay attention to this weeks report. Like a canary in a coal mine, the hypersensitive Polar Regions may well experience the full force of global warming before the rest of the planet does. However, there is a second and bigger reason to pay attention. An unexpectedly rapid warming of the Arctic could also lead directly to greater climate change elsewhere on the planet.

　　G. Arctic warming may influence the global climate in several ways. One is that huge amounts of methane, a particularly potent greenhouse gas, are stored in the permafrost of the tundra. Although a thaw would allow forests to invade the tundra, which would tend to ameliorate any global warming that is going on , a melting of the permafrost might also lead to a lot of trapped methane being released into the atmosphere, more than offsetting the cooling effects of the new forests.

　　H. Another worry is that Arctic warming will influence ocean circulation in ways that are not fully understood. One link in the chain is the salinity of seawater, which is decreasing in the north Atlantic thanks to an increase in glacial melt waters. Because fresh water and salt water have different densities, this freshening of the ocean could change circulation patterns. said Dr. Thomson, a British climate expert. The most celebrated risk is to the mid-Atlantic Conveyor Belt, a current which brings warm water from the tropics to north-western Europe, and which is responsible for that regions unusually mild winters, he added. Some of the ACIAs experts are fretting over evidence of reduced density and salinity in waters near the Arctic that could adversely affect this current.

　　I. The biggest popular worry, though, is that melting Arctic ice could lead to a dramatic rise in sea level. Here, a few caveats are needed. For a start, much of the ice in the Arctic is floating in the sea already. Archimedess principle shows that the melting of this ice will make no immediate difference to the seas level, although it would change its albedo. Second, if land ice, such as that covering Greenland, does melt in large quantities, the process will take centuries. And third, although the experts are indeed worried that global warming might cause the oceans to rise, the main way they believe this will happen is by thermal expansion of the water itself.

　　J. Nevertheless, there is some cause for nervousness. As the ACIA researchers document, there are signs that the massive Greenland ice sheet might be melting more rapidly than was thought a few years ago. Cracks in the sheet appear to be allowing melt water to trickle to its base, explains Michael Oppenheimer, a climatologist at Princeton University who was not one of the reports authors. That water may act as a lubricant, speeding up the sheets movement into the sea. If the entire sheet melted, the sea might rise by 6-7 meters. But when will this kind of disastrous ice disintegration really happen? While acknowledging it this century is still an unlikely outcome, Dr. Oppenheimer argues that the evidence of the past few years suggests it is more likely to happen over the next few centuries if the world does not reduce emissions of greenhouse gases. He worries that an accelerating Arctic warming trend may yet push the ice melt beyond an irreversible on / off switch.

　　K. That is scary stuff, but some scientists remain unimpressed. Patrick Michaels, a climatologist at the University of Virginia, complains about the ACIAs data selection, which he believes may have produced evidence of spurious warming. He also points out, in a new book, that even if Arctic temperatures are rising, that need not lead directly to the ice melting. As he puts it, Under global warming, Greenlands ice indeed might grow, especially if the warming occurs mostly in winter. After all, warming the air ten degrees when the temperature is dozens of degrees below freezing is likely to increase snowfall, since warmer air is generally moister and precipitates more water.

　　L. Nils-Axel Morner, a Swedish climate expert based at Stockholm University, points out that observed rises in sea levels have not matched the IPCCs forecasts. Since this weeks report relies on many such IPCC assumptions, he concludes it must be wrong. Others acknowledge that there is a warming trend in the Arctic, but insist that the cause is natural variability and not the burning of fossil fuels. Such folk point to the extraordinarily volatile history of Arctic temperatures. These varied, often suddenly, long before sport-utility vehicles were invented. However, some evidence also shows that the past few millennia have been a period of unusual stability in the Arctic. It is just possible that the current period of warming could tip the delicate Arctic climate system out of balance, and so drag the rest of the planet with it.

　　M. Not everybody wants to hear a story like that. But what people truly believe is happening can be seen in their actions better than in their words. One of the reports most confident predictions is that the breakup of Arctic ice will open the region to long-distance shipping and, ironically, to drilling for oil and gas. It is surely no coincidence, then, that the Danish government, which controls Greenland, has just declared its intention to claim the mineral rights under the North Pole. It, at least, clearly believes that the Arctic ocean may soon be ice-free.

　　雅思阅读真题题源第四篇：人类文字进化史

　　History of Writing

　　Writing was first invented by the Sumerians in ancient Mesopotamia before 3,000 BC. It was also independently invented in Meso-America before 600 BC and probably independently invented in China before 1,300 BC. It may have been independently invented in Egypt around 3,000 BC although given the geographical proximity between Egypt and Mesopotamia the Egyptians may have learnt writing from the Sumerians.

　　There are three basic types of writing systems. The written signs used by the writing system could represent either a whole word, a syllable or an individual sound. Where the written sign represents a word the system is known as logographic as it uses logograms which are written signs that represent a word. The earliest writing systems such as the Sumerian cuneiform, Egyptian hieroglyphics and Mayan glyphs are predominantly logographics as are modern Chinese and Japanese writing systems. Where the written sign represents a syllable the writing system is known as syllabic. Syllabic writing systems were more common in the ancient world than they are today. The Linear A and B writing systems of Minoan Crete and Mycenaean Greece are syllabic. The most common writing systems today are alphabetical. These involve the written sign representing a single sound . The earliest known alphabetical systems were developed by speakers of semetic languages around 1700 BC in the area of modern day Israel and Palestine. All written languages will predominately use one or other of the above systems. They may however partly use the other systems. No written language is purely alphabetic, syllabic or logographic but may use elements from any or all systems.

　　Such fully developed writing only emerged after development from simplier systems. Talley sticks with notches on them to represent a number of sheep or to record a debt have been used in the past. Knotted strings have been used as a form of record keeping particularly in the area around the Pacific rim. They reached their greatest development with the Inca quipus where they were used to record payment of tribute and to record commercial transactions. A specially trained group of quipu makers and readers managed the whole system. The use of pictures for the purpose of communication was used by native Americans and by the Ashanti and Ewe people in Africa. Pictures can show qualities and characteristics which can not be shown by tally sticks and knot records. They do not however amount to writing as they do not bear a conventional relationship to language. Even so, the Gelb dictum , that At the basis of all writing stands the picture has been widely accepted.

　　An alternative idea was that a system by which tokens, which represented objects like sheep, were placed in containers and the containers were marked on the outside indicating the number and type of tokens within the container gave rise to writing in Mesopotamia. The marks on the outside of the container were a direct symbolic representation of the tokens inside the container and an indirect symbolic representation of the object the token represented. The marks on the outside of the containers were graphically identical to some of the earliest pictograms used in Sumerian cuneiform, the worlds first written language. However cuneiform has approximately 1,500 signs and the marks on the ouside of the containers can only explain the origins of a few of those signs.

　　The first written language was the Sumerian cuneiform. Writing mainly consisted of records of numbers of sheep, goats and cattle and quantites of grain. Eventually clay tablets were used as a writing surface and were marked with a reed stylus to produce the writing. Thousands of such clay tablets have been found in the Sumerian city of Uruk. The earliest Sumerian writing consists of pictures of the objects mentioned such as sheep or cattle. Eventually the pictures became more abstract and were to consist of straight lines that looked like wedges.

　　雅思阅读真题题源第五篇：生物技术防治病虫害

　　Biological Pest Control

　　A. Biological control is, generally, humans use of a specially chosen living organism to control a particular pest. This chosen organism might be a predator, parasite, or disease which will attack the harmful insect. It is a form of manipulating nature to increase a desired effect. A complete Biological Control program may range from choosing a pesticide which will be least harmful to beneficial insects, to raising and releasing one insect to have it attack another, almost like a living insecticide.

　　B. Biological control methods can be used as part of an overall Integrated Pest Management program to reduce the legal, environmental, and public safety hazards of chemicals. In addition, it may be a more economical alternative to some insecticides. Some biological control measures can actually prevent economic damage to agricultural crops. Unlike most insecticides, biological controls are often very specific for a particular pest. Other helpful insects, animals, or people can go completely unaffected or disturbed by their use. There is less danger of impact on the environment and water quality.

　　C. Biological control takes more intensive management and planning. It can take more time, require more record keeping, more patience, and sometimes more education or training. Successful use of biological control requires a greater understanding of the biology of both the pest and its enemies. Many natural enemies are very susceptible to pesticides, and using them successfully in an IPM program takes great care. In some cases, biological control may be more costly than pesticides. Often, the results of using biological control are not as dramatic or quick as the results of pesticide use. Most natural enemies attack only specific types of insects unlike broad-spectrum insecticides, which may kill a wide range of insects. Though often an advantage, this can also be a disadvantage.

　　D. Biological control uses naturally occurring predators, parasites and diseases to control pests. There are three main ways to use these natural enemies against unwanted insect pest populations. Classical Biological Control involves traveling to the country or area from which a newly introduced pest originated and returning with some of the natural enemies that attacked it and kept it from being a pest there. New pests are constantly arriving accidentally or intentionally. Sometimes they survive. When they come, their enemies are left behind. If they become a pest, introducing some of their natural enemies can be an important way to reduce the amount of harm they can do. Augmentation is a method of increasing the population of a natural enemy which attacks a pest. This can be done by mass producing a pest in a laboratory and releasing it into the field at the proper time. Another method of augmentation is breeding a better natural enemy which can attack or find its prey more effectively. Mass rearings can be released at special times when the pest is most susceptible and natural enemies are not yet present, or they can be released in such large numbers that few pests go untouched by their enemies. The augmentation method relies upon continual human management and does not provide a permanent solution unlike the importation or conservation approaches may. Conservation of natural enemies is an important part in any biological control effort. This involves identifying any factors that limit the effectiveness of a particular natural enemy and changing them to help the beneficial species. Conservation of natural enemies involves either reducing factors which interfere with the natural enemies or providing needed resources that help natural enemies.

　　E. In addition to the introduction of predators, several microbial pathogens are effective against nematodes. They consist of a microorganism as the active ingredient. They can control many different kinds of pests, although each separate active ingredient is relatively specific for its target pest . For example, there are fungi that control certain weeds, and other fungi that kill specific insects. The most widely used microbial pesticides are subspecies and strains of Bacillus thuringiensis, or BT. Each strain of this bacterium produces a different mix of proteins, and specifically kills one or a few related species of insect larvae. While some BTs control moth larvae found on plants, other BTs are specific for larvae of flies and mosquitoes. The target insect species are determined by whether the particular BT produces a protein that can bind to a larval gut receptor, thereby causing the insect larvae to starve.

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