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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.
Bark beetles______.
选项 A、are disappearing because of the increase of wildfires
B、are easily killed by woodpeckers and nuthatches
C、lay their eggs under the ground at the bottom of trees
D、have become able to survive the winter
答案D
解析 细节题。本文讲述了因为全球变暖，导致一种害虫在森林肆虐的情况。因为全球变暖，树木的树脂干枯，不能淹死入侵的害虫，导致害虫的繁殖量增大，幼虫死亡率降低，在森林中肆虐。故A错误。“Woodpeckers and nuthatches keep adultnumbers in check，but with warmer winters，beetle populations can quadruple in a year，outpacing their pursuers”，故它的天敌不能有效地控制虫害，B错误。由“The galleriesof eggs they lay inside the bark…”，可以看出他们把卵产在树皮下，故C错误。从“mild winters in Wyoming have helped the beetle larvae(幼虫)survive the season”中看出D正确。
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