2017年7月29日雅思考试阅读考试回忆及解析
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本文导航第1页A-D题第2页E-I题第3页参考答案 2017年7月29日雅思考试阅读考试回忆及解析 Passage 1： 题目：Going Bananas 题型：填空题3+人名理论配对7+判断题3 新旧程度：旧题 文章大意：香蕉的起源、发展与现状 参考文章： Going Bananas A. The world’s favourite fruit could disappear forever in 10 years’ time. The banana is among the world’s oldest crops. Agricultural scientists believe that the first edible banana was discovered around ten thousand years ago. It has been at an evolutionary standstill ever since it was first propagated in the jungles of South-East Asia at the end of the last ice age. Normally the wild banana, a giant jungle herb called Musa acuminate, contains a mass of hard seeds that make the fruit virtually inedible. But now and then, hunter-gatherers must have discovered rare mutant plants that produced seed-less, edible fruits. Geneticists now know that the vast majority of these soft-fruited plants resulted from genetic accidents that gave their cells three copies of each chromosome instead of the usual two. This imbalance prevents seeds and pollen from developing normally, rendering the mutant plants sterile. And that is why some scientists believe the world’s most popular fruit could be doomed. It lacks the genetic diversity to fight off pests and diseases that are invading the banana plantations of Central America and the small-holdings of Africa and Asia alike. B. In some ways, the banana today resembles the potato before blight brought famine to Ireland a century and a half ago. But ‘it holds a lesson for other crops, too’, says Emile Frison, top banana at the International Network for the Improvement of Banana and Plantain in Montpellier, France. ‘The state of the banana’, Frison warns, ‘can teach a broader lesson the increasing standardization of food crops round the world is threatening their ability to adapt and survive.’ C. The first Stone Age plant breeders cultivated these sterile freaks by replanting cuttings from their stems. And the descendants of those original cuttings are the bananas we still eat today. Each is a virtual clone, almost devoid of genetic diversity. And that uniformity makes it ripe for disease like no other crop on Earth. Traditional varieties of sexually reproducing crops have always had a much broader genetic base, and the genes will recombine in new arrangement in each generation. This gives them much greater flexibility in evolving responses to disease – and far more genetic resources to draw on in the face of an attack. But that advantage is fading fast, as growers increasingly plant the same few, high-yielding varieties. Plant breeders work feverishly to maintain resistance in these standardized crops. Should these efforts falter, yields of even the most productive crop could swiftly crash. ‘When some pest or disease comes along, severe epidemics can occur,’ says Geoff Hawtin, director of the Rome-based International Plant Genetic Resources Institute. D. The banana is an excellent case in point. Until the 1950s, one variety, the Gros Michel, dominated the world’s commercial banana business. Found by French botanists in Asian the 1820s, the Gros Michel was by all accounts a fine banana, richer and sweeter than today’s standard banana and without the latter’s bitter aftertaste when green. But it was vulnerable to a soil fungus that produced a wilt known as Panama disease. ‘Once the fungus gets into the soil it remains there for many years. There is nothing farmers can do. Even chemical spraying won’t get rid of it,’ says Rodomiro Ortiz, director of the Inter-national Institute for Tropical Agriculture in Ibadan, Nigeria. So plantation owners played a running game, abandoning infested fields and moving so ‘clean’ land – until they ran out of clean land in the 1950s and had to abandon the Gros Michel. Its successor and still the reigning commercial king, is the Cavendish banana, a 19th century British discovery from southern China. The Cavendish is resistant to Panama disease and, as a result, it literally saved the international banana industry. During the 1960s, it replaced the Gros Michel on supermarket shelves. If you buy a banana today, it is almost certainly a Cavendish. But even so, it is a minority in the world’s banana crop. 相关资料 |
