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  3. As the earth’ s surfaces warm, evaporation(蒸发)is drying out forests and soils, increasing susceptibility to fire. Last summer, m

As the earth’ s surfaces warm, evaporation(蒸发)is drying out forests and soils, increasing susceptibility to fire. Last summer, m

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问题     As the earth’ s surfaces warm, evaporation(蒸发)is drying out forests and soils, increasing susceptibility to fire. Last summer, more than 7.3 million acres of U.S. forests burned during an intense drought. Most alarmingly, as an intergovernmental panel concluded in 2001, earth’ s biological systems are already responding to climate change. The current epidemic(传染病)of bark beetles adds a new dimension to the risk of fires.
    Mountain bark beetles attack lodgepole, ponderosa(黄松), Douglass fir(枞木), sugar and western white pines, destroying them by injecting a fungus(真菌). The galleries of eggs they lay inside the bark pave the way for the trees’ death within a year. Healthy trees secrete pitch to drown the invaders and plug the holes they bore, but drought dries out the pitch. Woodpeckers and nuthatches keep adult numbers in check, but with warmer winters, beetle populations can quadruple in a year, outpacing their pursuers.
    Warming is increasing the reproduction, abundance and geographic range of beetles, destabilizing the age-old, hard won truce between insects and vegetation. Since 1994, mild winters in Wyoming have helped the beetle larvae(幼虫)survive the season. Usually, 80 percent die, but the mortality rate has dropped to less than 10 percent. In Alaska, spruce bark beetles are sneaking in an extra generation a year due to warming, and have destroyed 4 million acres in the Kenai Peninsula in the past five years. "This is another example of global climate change that has deadly implications for my state," declared Alaska’s Republican Sen. Ted Stevens last year.
    Warming is also expanding the beetles’ range into higher altitudes. In the past four or five years, they have begun to attack whitebark pines at an elevation of 8,000 feet or higher. Jesse Logan, who works for the Utah Forest Service, told the Billings(Mont.)Gazette last month that this development coincides with an overall wanning trend that began in the 1980s. "Beetles are cold-blooded, so their metabolism is related to the environment they’re in," according to Logan, who said the beetles seem to be a reliable indicator of global climate change.
What is the relationship between bark beetles and climate change?
选项 A、More and more bark beetles die due to global wanning.
B、Bark beetles have more risk of dying in warming winters.
C、Global warming causes an increase in the number of bark beetles.
D、There is no relation between them.
答案C
解析 细节题。从上题的解析中可以看出，气候变暖对于这种害虫的繁衍有利．暖冬可以使他们的死亡率降低，故A、B、D错误。他们的关系是变暖可以导致害虫数量的增长。
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