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盾皮鱼类(Placodermi)是大约3.95亿年前出现于泥盆纪早期的另一类______鱼类，被认为是______的祖先。
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根据下面资料，回答下列各题 It would be all too easy to say that Facebooks market meltdown
根据以下内容，回答下列各题。 Genetically Modified Foods--Feed the World？ [A] Ifyou want to spark a heated debate at a dinner party, bring up the topic about genetically modifiedfoods. For many people, the concept of geneticallyaltered, high-tech crop production raises all kinds of environmental, health, safetyand ethical questions. Particularly in countries with long agrariantraditions--and vocal green lobbies--the idea seems against nature. [B] Infact, genetically modified foods are already very much a part of our lives. Athird of the corn and more than half the soybeans and cotton grown in the U. S. last year were the product of biotechnology,according to the Department of Agriculture. More than 65 million acres ofgenetically modified crops will be planted in the U. S. this year. The geneticis out of the bottle. [C] Yetthere are clearly some very real issues that need to be resolved. Like any newproduct entering the food chain, genetically modified foods must be subjectedto rigorous testing. In wealthy countries,the debate about biotech is tempered by the fact that we have a rich array offoods to choose from--and a supply that far exceeds our needs. In developingcountries desperate to feed fast-growing and underfed populations; the issue issimpler and much more urgent: Do the benefits of biotech outweigh the risks？ [D] Thestatistics on population growth and hunger are disturbing. Last year theworlds population reached 6 billion. And by 2050, the UN estimates, it will beprobably near 9 billion. Almost all that growth will occur in developingcountries. At the same time, the worlds available cultivable land per personis declining. Arable land has declined steadily since 1960 and will decrease byhalf over the next 50 years, according to the International Service for theAcquisition of Agri-Biotech Applications (ISAAA). How can biotech help？ [E]Biotechnologists have developed genetically modified rice that is fortifiedwith beta-carotene(β-胡萝卜素)--which the body converts into vitaminA--and additional iron, and they are working on other kinds of nutritionallyimproved crops. Biotech can also improve farming productivity in places where foodshortages are caused by crop damage attribution to pests, drought, poor soiland crop viruses, bacteria or fungi (真菌 ). [F]Damage caused by pests is incredible. The European corn borer, for example,destroys 40 million tons of the-worlds corn crops annually, about 7% of thetotal. Incorporating pest-resistant genes into seeds can help restore thebalance. In trials of pest-resistant cotton in Africa, yields have increased significantly.So far, fears that genetically modified, pest-resistant crops might kill goodinsects as well as bad appear unfounded. [G]Viruses often cause massive failure in staple crops in developing countries.Two years ago, Africa lost more than half its cassava (树薯) crop--a key source ofcalories-to the mosaic virus (花叶病毒).Geneticallymodified, virus-resistant crops can reduce that damage, as can drought-tolerantseeds in regions where water shortages limit the amount of land under cultivation.Biotech can also help solve the problem of soil that contains excess aluminum,which can damage roots and cause many staple-crop failures. A gene that helpsneutralize aluminum toxicity (毒性) in rice has beenidentified. Many scientists believe biotech could raise overall cropproductivity in developing countries as much as 25% and help prevent the lossof those crops after they are harvested. [H]Yetfor all that promise, biotech is far from being the whole answer. In developingcountries, lost crops are only one cause of hunger. Poverty plays the largestrole. Today more than 1 billion people around the globe live on less than 1dollar a day. Making genetically modified crops available will not reducehunger if farmers cannot afford to grow them or if the local population cannotafford to buy the food those farmers produce. [I]Biotech has its own "distribution" problems. Private-sector biotechcompanies in the rich countries carry out much of the leading-edge research ongenetically modified crops. Their products are often too costly for poorfarmers in the developing world, and many of those products wont even reachthe regions where they are most needed. Biotech firms have a strong financialincentive to target rich markets first in order to help them rapidly recoup thehigh costs of product development. But some of these companies are respondingto needs of poor countries. [J] Moreand more biotech research is being carried out in developing countries. But toincrease the impact of genetic research on the food production of thosecountries, there is a need for better collaboration between governmentagencies--both local and in developed countries--and private biotech firms. TheISAAA, for example, is successfully partnering with the U. S. Agency for InternationalDevelopment, local researches and private biotech companies to find and deliverbiotech solutions for farmers in developing countries. Will"Franken-foods" feed the world？ [K]Biotechis not a panacea (治百病的药), but it does promise to transform. agriculture in many developingcountries. If that promise is not fulfilled, the real losers will be theirpeople, who could suffer for years to come. [L] Theworld seems increasingly to have been divided into those who favor geneticallymodified foods and those who fear them. Advocates assert that growinggenetically altered crops can be kinder to the environment and that eatingfoods from those plants is perfectly safe. And, they say, genetic engineering--whichcan induce plants to grow in poor soils or to produce more nutritious foods—willsoon become an essential tool for helping to feed the worlds burgeoning(迅速发展的) population. Skepticscontend that genetically modified crops could pose unique risks to theenvironment and to health--risks too troubling to accept placidly. Taking thatview, many European countries are restricting the cultivation and importationof genetically modified agricultural products. Much of the debate are concernedabout of safety. But what exactly does recent scientific research say about thehazards？ [M] Twoyears ago in Edinburgh, Scotland, eco-vandals stormed a field, crushing canolaplants. Last year in Maine, midnight raiders hacked down more than 3,000experimental poplar trees. And in San Diego, protesters smashed sorghum andsprayed paint over greenhouse walls. This far-flung outrage took aim atgenetically modified crops. But the protests backfired: all the destroyedplants were conventionally bred. In each case, activists mistook ordinaryplants for genetically modified varieties. [N] Itseasy to understand why. In a way, genetically modified crops--now on some 109million acres of farmland worldwide--are invisible. You cant see, taste ortouch a gene inserted into a plant or sense its effects on the environment. Youcant tell, just by looking, whether pollen containing a foreign gene canpoison butterflies or fertilize plants miles away. That invisibility isprecisely what worries people. How, exactly, will genetically modified cropsaffect the environment--and when will we notice？ [O]Advocates of genetically modified or transgenic crops say the plants willbenefit the environment by requiring fewer toxic pesticides than conventionalcrops. But critics fear the potential risks and wonder how big the benefits reallyare. "We have so many questions about these plants," remarks GuentherStotzky, a soft microbiologist at New York University. "Theres a lot wedont know and need to find out. "As genetically modified crops multiplyin the landscape, unprecedented numbers of researchers have started fanninginto the fields to get the missing information. Some of their recent findingsare reassuring; others suggest a need for vigilance. According to the UNs prediction, the population growth from now to 2050 is nearlyall in developing countries.
肌肉收缩是______在______之间主动地相对______的结果。
宏观和微观领域的研究成果导致了对达尔文学说的怎样修正？
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