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  3. Britain’s east midlands were once the picture of English countryside, alive with flocks, shepherds, skylarks and buttercups—the

Britain’s east midlands were once the picture of English countryside, alive with flocks, shepherds, skylarks and buttercups—the

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问题     Britain’s east midlands were once the picture of English countryside, alive with flocks, shepherds, skylarks and buttercups—the stuff of fairytales. In 1941 George Marsh left school at the age of 14 to work as a herdsman in Nottinghamshire, the East Midlands countryside his parents and grandparents farmed. He recalls skylarks nesting in cereal fields, which when accidentally disturbed would fly singing into the sky. But in his lifetime, Marsh has seen the color and diversity of his native land fade. Farmers used to grow about a ton of wheat per acre; now they grow four tons. Pesticides have killed off the insects upon which skylarks fed, and year-round harvesting has driven the birds from their winter nests. Skylarks are now rare. "Farmers kill anything that affects production," says Marsh. "Agriculture is too efficient. "
    Anecdotal evidence of a looming crisis in biodiversity is now being reinforced by science. In their comprehensive surveys of plants, butterflies and birds over the past 20 to 40 years in Britain, ecologists Jeremy Thomas and Carly Stevens found significant population declines in a third of all native species. Butterflies are the furthest along—71 percent of Britain’s 58 species are shrinking in number, and some, like the large blue and tortoiseshell, are already extinct. In Britain’s grasslands, a key habitat, 20 percent of all animal, plant and insect species are on the path to extinction. There’s hardly a corner of the country’s ecology that isn’t affected by this downward spiral.
    The problem would be bad enough if it were merely local, but it’s not : because Britain’s temperate ecology is similar to that in so many other parts of the world, it’s the best microcosm scientists have been able to study in detail. Scientists have sounded alarms about species’ extinction in the past, but always specific to a particular animal or place—whales in the 1980s or the Amazonian rain forests in the 1990s. This time, though, the implications are much wider. The Amazon is a "biodiversity hot spot" with a unique ecology. But in Britain, "the main drivers of change are the same processes responsible for species’ declines worldwide, "says Thomas. The findings, published in the journal Science, provide the first clear evidence that the world is in the throes of a massive extinction. Thomas and Stevens argue that we are facing a loss of 65 to 95 percent of the world’s species, on the scale of an ice age or the meteorite that may have wiped out the dinosaurs 65 million years ago.
    If so, this would be only the sixth time such devastation had occurred in the past 600 million years. The other five were associated with one-off events like the ice ages, a volcanic eruption or a meteor. This time, ecosystems are dying a thousand deaths—from overfishing and the razing of the rain forests, but also from advances in agriculture. The British study, for instance, finds that one of the biggest problems is nitrogen pollution. Nitrogen is released when fossil fuels burn in cars and power plants—but also when ecologically rich heath-lands are plowed and fertilizers are spread. Nitrogen-rich fertilizers fuel the growth of tall grasses, which in turn overshadow and kill off delicate flowers like harebells and eyebrights.
    Even seemingly innocuous practices are responsible for vast ecological damage. When British farmers stopped feeding horses and cattle with hay and switched to silage, a kind of preserved short grass, they eliminated a favorite nesting spot of corncrakes, birds known for their raspy nightly mating calls; corncrake populations have fallen 76 percent in the past 20 years. The depressing list goes on and on.
    Many of these practices are being repeated throughout the world, in one form or another, which is why scientists believe that the British study has global implications. Wildlife is getting blander. "We don’t know which species are essential to the web of life so we’re taking a massive risk by eliminating any of them," says David Wedin, professor of ecology at the University of Nebraska. Chances are we’ll be seeing the results of this experiment before too long.
What is the difference between today’s ecological change and the five changes in ancient times?
选项 A、Species like the dinosaurs brought the ice ages to an end.
B、A volcanic eruption might lead to a great catastrophe.
C、Today’s change is mainly caused by agricultural advances.
D、Today’s change attributes to a multitude of reasons.
答案D
解析 细节题。由题干中的five定位至第四段。第二句指出：其他五次灾难的发生与某一事件有 关，例如冰川时代、火山爆发或流星的出现。而第三句提到这次生态系统面临的问题非常 多：过度捕鱼，雨林被摧毁，农业的发展等。[D]符合文意，故为答案。[B]虽然符合逻辑，但 并非文章提到的区别，排除。  
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