Text 1

Environmental Problems

  The development of science and technology in the twentieth century has greatly raised the quality of human life but at the same time it has also led to some serious problems threatening the survival of human beings. Among these are issues concerning environmental protection. Do you know what the greenhouse effect is? What is acid rain or the ozone hole? The following passage discusses some of the environmental problems and the ways to solve them.

  Before humans came on the scene, the world changed only slowly. The climate warmed and cooled, new plants and animals evolved and became extinct in their turn, and sea levels rose and fell over periods of thousands, if not millions, of years. But during the last two thousand years there have been very great changes. Forests have disappeared, river courses have been changed, and large areas of natural vegetation have turned into farmland and cities. There are serious problems for the survival of the human race.

    The greenhouse effect It may be cold outside, but on a sunny day it can be hot in a greenhouse. Some of the gases in the Earth's atmosphere act like the glass in a greenhouse. Radiant heat from the Sun can pass through them to warm the Earth below. But the ground also loses heat by radiation. The "greenhouse gases" send some of this heat back towards the Earth's surface and help to keep it warm. However, by burning fuels and forests, we are putting larger and larger amounts of these greenhouse gases into the atmosphere. As a result, the Earth is slowly warming up. This is called the greenhouse effect.

    Greenhouse gases Carbon dioxide is the main greenhouse gas in the atmosphere. Animals (like ourselves) give out carbon dioxide when they breathe, while plants breathe in carbon dioxide. In this way, animals and plants keep the atmosphere in balance and the amount of carbon dioxide stays the same.

    However, our modern life-style is destroying the balance. When we burn fuels in vehicles and power-stations, huge amounts of extra carbon dioxide go into the atmosphere. In some countries people are burning vast areas of tropical rainforest and opening land for development or cattle-rearing. This is causing a double problem. The burning is releasing more carbon dioxide and the Earth is left with fewer plants to breathe in the gas.

    There are several other greenhouse gases in the atmosphere. Methane comes from animal waste, swamps, rice paddy-fields, and oil and gas rigs. Nitrous oxide comes from car exhausts and from chemical fertilizers. Chlorofluorocarbons (CFCs) have been used in refrigerators and freezers. Amounts of CFCs in the atmosphere are small, but these gases are 10 000 times more effective than carbon dioxide at trapping heat.

    Solving the problem The problem with the greenhouse effect began about 100 years ago when people started using fuels like oil and petrol on a large scale. On average, world temperatures have risen by about half a degree (Celsius) over the last 100 years. They could rise by another three degrees over the next 50 years. This may not sound very much. But it could cause dry weather in some parts of the world. If the polar ice-caps melt and sea-levels rise, many areas of the world will be flooded.

    Scientists believe that the only way to slow the greenhouse effect is for us to produce less of the gases which cause it. Governments are already trying to reduce the use of CFCs. We need to use less fuels like petrol, oil, natural gas and coal. We can develop heating systems and engines which burn fuel more efficiently. And we can build houses and offices which waste less heat, and transport systems which need fewer vehicles. We can also use sources of power that do not burn fuel and release carbon dioxide. Nuclear power is one possibility, but many people are worried about the dangers of using this. Other alternatives are wind, water, and geothermal power.

    Air pollution and acid rain Pollution is caused when what we do damages our surroundings. Factories, power-stations and motor vehicles send waste gases and soot into the air. The polluted air damages people's lungs. Some petrol has lead in it. The lead comes out in car exhaust fumes and it can cause brain damage in children.

    The waste gases coming from burning coal, oil and petrol include sulphur dioxide and nitrogen dioxide. These gases may dissolve in water in the atmosphere to form weak acids. They later fall to the Earth as acid rain, sometimes hundreds of kilometers from where they were formed. Much of the acid rain in Canada is caused by smoke from factories and power-stations in the USA; the acid rain in Scandinavia may come from Britain.

    Acid rain attacks trees and other plants, and kills the fish and water animals living in lakes and rivers. Acid rain and polluted air also damage the bricks and stonework of buildings, and corrode the metalwork of steel bridges and railings.

    Preventing acid rain Acid rain is difficult to control because it spreads so far. Building tall chimneys reduces the effect near the factory, but passes the pollution on to other areas. There are some types of coal and oil which have very little sulphur in them. The waste gases of factories and power-stations can also be cleaned before they leave the factory, and cars can use devices to clean their exhaust smoke. These methods are all expensive.

    The ozone hole Ozone is a gas which forms a layer around the planet at about 20 to 50 km (6 to 30 miles) above the Earth's surface. The ozone layer prevents the Sun's dangerous ultraviolet radiation reaching the Earth where it would damage our skin and cause cancers. Many scientists are worried that the ozone layer is being destroyed by the CFCs which are used in refrigerators and freezers. These chemicals are also important greenhouse gases. At certain times of the year the ozone layer becomes extremely thin near the north and south poles. Already skin cancers are increasing in Australia.

    Many countries are trying to stop the production of CFCs and to find other chemicals to do the same thing.

    Pollution of rivers, lakes and the sea Air pollution affects rivers and lakes indirectly because it causes acid rain. But rivers may also be polluted directly. Some towns and villages send waste material and waste water into rivers, while factories sometimes release poisonous wastes into the water.Fertilizers and chemical pesticides used by farmers can also be washed by rainwater into rivers and streams. They can kill fish and other water animals and plants.

    Rivers eventually flow into the sea, carrying their pollution with them. But the sea can also be polluted directly. Some coastal towns and cities send their waste water straight into the sea, killing seabirds, shellfish and other wildlife.

    All power-stations need huge amounts of water to cool them. This is taken from rivers, lakes or the sea. When it is returned the water is warmer than it was originally. Warm water does not hold as much oxygen as cold water, so it harms animals. It may kill fish and other water animals in the immediate area or prevent them from breeding.

    Radioactive waste Nuclear power-stations produce waste which is radioactive. Some of this waste is released by the power-stations into the air or water; some is stored. It can be carried long distances by wind or by water. Many scientists worry about the long-term effects of this type of pollution on humans and wildlife.

    (1 186 words)

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课文一

环境问题

    20世纪的科技发展大大提高了人类的生活质量,但同时也引发了一些严重的问题,威胁着人类的生存。其中有些问题与环境保护有关。你知道什么是温室效应吗？什么是酸雨？什么是黑洞？下面这篇文章讨论了一些环境问题及其解决办法。

    人类出现以前，世界变化非常缓慢。气候变暖又转冷，新的植物、动物进化又渐次灭亡，海平面上升而后下降，这样的变化如果不是需要数百万年的时间，也是需要数千年的时间的。然而，在过去的两千年间，世界的变化非常显著。森林消失，河流改道，大片大片草木自然生长的地方变成了农场和城市。人类的生存面临着严峻的问题。

    温室效应
     温室外面也许很冷，但晴天时室内就会很热。地球大气层中的一些气体起着类似温室玻璃的作用。太阳辐射热可以穿过这些气体使地球变暖。不过地面也会通过辐射散发热量。“温室气体”把热量辐射回地球表面，使之保温。然而，由于不断地燃烧燃料、烧毁森林，我们正在把越来越多的温室气体释放到大气层。结果，地球在逐渐变暖。这就是温室效应。

    温室气体
    二氧化碳是大气层中主要的温室气体。动物（和我们一样）呼吸时呼出二氧化碳，植物吸入二氧化碳。这样，动物和植物保持着大气的平衡，二氧化碳的总量不变。

     然而，我们的现代生活方式正在破坏着这种平衡。当我们把燃料用于车辆和火电厂时，大量多余的二氧化碳进入大气层。在一些国家里，人们在烧毁大片大片的热带森林，开拓土地用于发展和畜牧。这样的做法引起双重的问题：燃烧释放出的二氧化碳越来越多，地球上吸收二氧化碳的植物越来越少。

     大气层中还有其他几种温室气体。甲烷产生于动物的粪便、沼泽、水稻田以及油井和天然气钻塔。一氧化氮来自汽车废气和化学肥料。含氯氟烃（CFCs）一直用于冰箱和冷库。大气层中CFCs的数量虽不多，但它比二氧化碳吸存的热量要高一万倍。

     解决问题
    大约在一百多年前，当人们开始广泛用石油、汽油作燃料，温室效应的问题开始出现。过去一百年间世界各地的气温平均上升了半度（摄氏度）左右。未来五十年间气温还要上升3度。听起来不算多，但是这3度能使世界上一些地方出现干旱。如果极地的冰层融化，海面升高，那么，世界许多地区就会被淹没。

　

   科学家们认为，我们减缓温室效应的唯一途径就是要减少排放导致温室效应的气体。各国政府正尽力减少使用CFCs。我们必须少用汽油、燃油、天然气和煤这类燃料。我们可以改良供暖系统和发动机，使燃料更充分地燃烧。我们还可以修建节能的住所和写字楼，建设需要较少车辆的运输系统。我们也可以使用无需燃烧、不会释放二氧化碳的能源。原子能是一种选择，但是许多人担心使用它会带来危险。其他可供选择的能源有风力，水力和地热。

    大气污染和酸雨
    当我们的行为破坏了周围的环境时，污染就产生了。工厂、火电站和机动车辆将废气、烟灰排放到大气中。被污染的大气危害人们的肺部健康。某些汽油中含铅，铅随汽车废气排出，会损伤儿童的大脑。

    煤、燃油和汽油燃烧时产生的废气中含有二氧化硫和二氧化氮。这些气体溶于大气层中的水汽，形成弱酸。它们以酸雨的形式降到地球上，有时离酸雨形成的地区有千里之遥。降在加拿大的大多数酸雨，就是美国的工厂和火电站的烟尘引发的；斯堪的那维亚半岛的酸雨可能源自英国。 

    酸雨侵袭树木和其他植物，杀死湖泊河流里的鱼类以及水生动物。酸雨和被污染的大气还会侵蚀建筑物的砖块和石造的部分，腐蚀钢制桥梁和铁轨的金属部分。

    防止酸雨
   酸雨之所以难以控制，是因为它的覆盖范围相当广。建造高耸的烟囱虽然减轻了废气对工厂附近地区的危害，却把污染带到其他地区。可以使用一些含硫量极少的煤和石油。可以在工厂和火电站的废气出厂前进行污处理，汽车上可以使用净化废气的装置。但是，这些办法都耗资巨大。

    黑洞
    臭氧是一种气体,它在离地球表面约20至50公里（6至30英里）处形成一层环绕地球的大气层。臭氧层阻止有害的太阳紫外线到达地球，损伤我们的皮肤，引发癌症。许多科学家担心臭氧层正遭到冰箱和冰库中使用的CFCs的破坏。这些含氯氟烃化学物质也是主要的温室气体。一年中的某些时候，北极和南极附近地区的臭氧层极为稀薄。澳大利亚的皮肤癌病例已在不断增加。

     许多国家正准备停止生产CFCs，用其它的化学品来替代。

    河流、湖泊和海洋的污染
    由于大气污染引起酸雨，所以大气间接地影响了河流和湖泊。但是河流也会受到直接污染。一些城镇和村庄把污物和污水直接排放到河里；工厂有时也把有毒的废弃物排放到水里。农田里的化肥和化学杀虫剂也会被雨水冲到河里，毒死鱼类和其它的水生动植物。

    河流最终流入海洋，污染物也随之入海。然而，海洋也会受到直接污染。一些沿海城镇把污水直接排入大海，导致了海鸟、贝类和其它野生物的死亡。

    为了冷却，所有的火电站都需要大量的用水。这些水来自河流、湖泊或大海。但是，当用水排回河里时，水温升高，水中所含的氧气比冷水含的少，因此对动物十分有害。污水源附近的鱼类和其它水生动物可能会死掉或无法繁殖。

    放射性废弃物
    核电站排出放射性的废弃物。一部分废弃物进入空气或水中；一部分留在核电站。废气物能够随风或者随水漂流到遥远的地方。许多科学家担心这种污染物会长期影响人类和野生动物。

    （1186个单词）

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Text 2

Farming

    Most types of farming produce food for people to eat. Farmers make the best use they can of natural resources (such as soil and climate) to produce crops and rear animals. Different types of plants and animals need different conditions to grow well in and there is a variety of types of farming around the world.

    Dairy farming and mixed farming Dairy farming produces milk, butter and cheese from cows that graze in grassy fields. Dairy farms are usually quite close to large cities so that fresh milk can quickly reach people's kitchens.

    Mixed farming involves both crops and livestock. The main area is the cornbelt of the midwest USA. Here farmers grow corn to feed pigs and cattle. Oats and hay are also grown as feed, as well as other crops such as soy beans and wheat. Mixed farming is found in Europe, too, in a region that stretches from northern Portugal and Spain across France, Germany and Poland and into Russia. In Britain mixed farms are found from Devon across the counties of the Midlands.

    Mediterranean farming is found in areas with a Mediterranean climate where winters are mild, summers long and dry and rainfall is quite low. These areas are around the Mediterranean Sea, and also in California, Chile, South Africa and Australia. Winter crops include wheat and barley. Summer crops include peaches, citrus fruits, tomatoes, grapes and olives.

    Shifting cultivation is a common type of farming in many tropical countries. It is different from settled farming because shifting cultivators raise crops in a place for only as long as the soil allows the crops to grow well. After a year or so in one place the farmer moves on, cuts the natural vegetation from another area, and leaves the first plot to return to its natural state. Shifting cultivation is practiced in the tropical forests of Central and South America, Africa and south-east Asia. Farmers grow maize, rice, manioc, yams, millet and other food crops.

    Pastures and cattle ranges Much of the beef in hamburgers eaten in North America comes from cattle that graze in Central and South America. To expand cattle-ranching, tropical forests have been cut down to provide grasslands for "hamburger cattle". Cattle also graze on natural grasslands such as the pampas of Argentina, where cattle have been herded by "gauchos" on horseback for more than a hundred years.

    In countries where intensive farming is practiced, such as Britain, some cattle are not only fattened on pastures. They are also injected with drugs that make their bodies produce more meat. Where this is not done the farming is "extensive" rather than "intensive", as quite large areas of grassland are needed to fatten one cow. In parts of East Africa where grasslands are not good enough to feed cattle all the year round, farmers have to move their herds with the seasons to find new grasslands.

    Farm animals Sheep, cattle, pigs, chickens and goats are all farm animals. Sheep are kept both for their meat and for their wool. A farmer or shepherd leaves sheep to graze on grasslands. Dogs often help to round up the sheep and to protect them and their lambs from wild animals such as wolves and eagles. Sheep are often reared on grasslands that cannot be used for other types of farming because they are too steep or too dry. Lamb and mutton are popular meats in many regions of the Middle East. You would rarely see pigs kept on farms in the Middle East, however, because most people there are Muslims and do not eat pork. Chickens are found on farms in many regions of the world. In Western Europe and North America large numbers of chickens are kept indoors in row upon row of small cages, often never seeing the light of day. The farmer feeds these "battery hens" each day and collects their eggs.    

    Intensive farming Battery hens are an example of intensive farming: farmers organize their animals and crops to get the maximum food from them. Intensive farming uses a lot of machinery to make it more efficient. Tractors are used to plough fields and plant seeds, and chemical fertilizers make plants grow stronger, while pesticides kill pests and herbicides kill weeds. In North America the wheat belt, stretching from the USA into the Canadian prairies, is a large area of intensive farming where the wheat is harvested with combine harvesters.

    Grain farming Grain (cereals) is the most important food source for most people in the world. The main types of grain are wheat, corn (maize), and rice. The USA, Argentina, Australia and Russia are the main world areas of wheat production. Farming in these countries is mostly intensive. Farmers use machines, fertilizers, pesticides and herbicides on large wheat fields. This intensive farming means that the amount of grain produced from a hectare of field (its "yield") in North America is over four times that produced from a hectare in Africa. The USA is the world's biggest exporter of grain. Nearly every African country imports grain. Grain is also used for animal fodder.

    The Green Revolution In the 1960s special international efforts were made to breed new crop varieties that would produce better yields. This would produce more food from an average field to feed the fast-growing populations of tropical countries. Scientists were successful in breeding high-yield types of wheat and rice. This has become known as the "Green Revolution". In India, China, Mexico, the Philippines and other parts of south-east Asia the production of these foods has risen quickly. Some of the new rice types, for example, yield three times as much rice per hectare as traditional types. They also grow more quickly, allowing two or three crops a year from land that used to produce only one crop.

    There are problems, however. The new varieties of plants need fertilizers and pesticides if they are to grow well and resist diseases. Not all farmers can afford these chemicals, which also cause pollution of soil and water.

    Organic farming Farmers who choose to farm organically do not use chemicals on their land. Fertilizers, pesticides and herbicides can cause problems. They kill plants and animals that the farmer does not want to kill, and very small traces of the chemicals may be left in crops, which may make them dangerous to eat.

    Organic farming uses compost and manure from farm animals to fertilize the land, and other plants, such as garlic, to control insects. Animals kept on organic farms are allowed to roam in the open air and are not locked up in cages for long periods. Organic farming has grown in the USA and Europe as farmers have realized some of the problems of intensive farming. Many people believe that food grown organically tastes better and is safer than food produced by intensive methods.

    Farms of the future Some of the problems of poor weather can be solved by breeding special new crops that are not so spoiled by frost or certain pests. This sort of breeding, using "plant genetics", is going to become more and more common in farming in the future.

    (1190 words) TOP

课文二

农场经营

    大多数农场为人们生产食物。农场主们尽其所能地利用自然资源（如土壤和气候），种植作物，饲养动物。不同种类的植物和动物需要不同的生长条件，因此世界各地有各式各样的农场经营方式。

    乳品业和混合业 乳品业依靠牧场放牧的奶牛生产牛奶，黄油和奶酪。通常奶场距离大城市很近，新鲜牛奶能够迅速送到订户的厨房。

    混合业包括作物种植和畜牧业。主要经营区是美国中西部的玉米带。这里的农场主种植玉米是为了养猪喂牛。种燕麦和干草也是来做饲料用的，其他作物，如大豆和小麦，也是如此。欧洲也有一个混合农场经营区：从西班牙和葡萄牙北部跨越法国、德国和波兰，直到俄罗斯境内。英国的混合业农场是从德文郡到中部高地的各郡。

    地中海式农场经营的地区属于地中海气候，冬季温和，夏季漫长、干燥少雨。这些经营区环绕在地中海沿岸，加利福尼亚、智利、南非、和澳大利亚也有。冬季作物有小麦和大麦。夏季作物有桃、柑橘类水果、番茄、葡萄和橄榄。

    轮作耕种是许多热带国家常见的农场经营方式。它不同于固定的耕种，因为轮作耕种者在一个地方种庄稼的时间长短要视那里的土壤适合庄稼生长的时间而定。在一个地方种了一年左右，农场主就继续迁移，把另一片地的草木砍掉，种上庄稼，让第一块地恢复到自然状态。在中南美洲、非洲和东南亚的热带森林地区也采用轮作式耕种。农场主们种植玉米、水稻、树薯、山药、小米和其他的粮食作物。

     牧场和养牛场 北美人吃的汉堡中，牛肉大多来自中美洲和南美洲的牛群。为了扩大养牛场，人们砍掉热带森林，用作“汉堡牛”的草场。牛群也放牧在天然草场上，如阿根廷的南美大草原，那儿的“南美牧人”骑在马背上放牛的历史已有一百多年了。

    一些采用集约化经营的国家，如英国，催使牛群肥壮不单单靠放牧。人们还给牛注射药物，提高牛肉产量。未采用这种方法的农场经营是分散型的，而不是集约型，因为养肥一头奶牛需要相当面积的大草场。东非一些地区的草场不能全年供牛群食用，牧场主们不得不随季节的更替赶着牛羊寻找新的草场。

    农场饲养的动物 绵羊、牛、猪、鸡和山羊都是农场饲养的动物。绵羊不仅可以产肉还能产毛。牧场主或牧羊人让绵羊在草场上吃草。牧羊狗常帮着主人圈赶羊群，保护羊群和羊羔免遭狼、鹰等野生动物的侵害。放牧绵羊的草场常常是一些地势陡峭或土壤过于干燥不能耕种其他作物的场地。中东许多地区的人们都爱吃羊羔肉和羊肉。但你很少看到他们的农场里养猪。因为那儿大多数人是穆斯林，所以他们不吃猪肉。全世界许多地区的农场都养鸡。西欧和北美的农场里，大批的鸡养在室内一排排层层叠放的小笼子里，常常一丝光亮也见不到。农场主每天给这些层架式鸡笼里的鸡喂食，拾取鸡蛋。

    集约化农场经营 层架式鸡笼养鸡就是集约化农场经营的一个例子：农场主们管理动物和庄稼，以得到最大产出。集约化农场使用许多机械设备，提高经营效率。拖拉机用来犁田、播种，化肥可以使植物长得更茁壮，杀虫剂可以杀死害虫，除草剂除去野草。北美的小麦种植带，从美国延伸到加拿大的大草甸，一大片地区都是集约化经营的农场，那儿的人们用联合收割机收割小麦。

    谷物耕作 谷物（谷类植物）是世界上大多数人的最重要的食物来源。主要的谷类有小麦、玉米和水稻。美国、阿根廷、澳大利亚和俄罗斯是世界上小麦的主要产区。这些国家的农场大多是集约化经营。农场主在大片大片的小麦田里使用机器、化肥、杀虫剂和除草剂，这种集约化耕种意味着北美一公顷田地生产的谷物量（产量）是非洲的四倍多。美国是世界最大的谷类出口国。非洲几乎所有国家都进口谷物。谷类还可用作动物饲料。

    绿色革命 20世纪60年代，国际上曾专门组织力量培育作物新品种，提高作物产量，使一块普通的田地能够生产出更多的粮食，满足热带国家快速增长的人口需要。科学家们成功地培育出高产的小麦和水稻品种。这就是著名的“绿色革命”。在印度、中国、墨西哥、菲律宾和东南亚的其他地区，新品种的粮食产量增长很快。例如，有些水稻新品种每公顷产量是传统品种的三倍。这些新品种生长迅速，以前只能收一季的田地现在可以一年收二至三季。

    然而也存在问题。植物新品种要想长得好，抵抗疾病，就需要化肥和杀虫剂。并非所有的农场主都能买得起这些化学品，而这些化学品也会引起土壤污染和水污染。

    有机耕种 施用有机肥耕种的农场主们不会在田间使用化学物品。化肥、杀虫剂和除草剂会产生种种问题：它们会杀死农场主们不想杀死的动植物；极少量的化学品可能残留在庄稼上，危及食用。

    有机耕种是用混合肥料和饲养的动物的粪便给田地施肥，并用其他的植物，如大蒜，来控制昆虫。在施用有机肥的农场上，动物在露天草场上放养，而不是长期被关在笼子里。美国和欧洲也渐渐兴起用有机肥施用农场，因为农场主们认识到了集约化农场经营的一些弊端。许多人认为施用有机肥产出的食物比集约方式生产的食物的味道更好、更安全。

    未来的农场 培育特殊的作物新品种可以解决坏天气带来的一些问题，不受霜冻或某些害虫的破坏。这种作物的培育运用了“植物遗传学”，将在未来的农场经营中越来越普遍。

    （1190个单词）

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