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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

admin2014-12-31  15
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 kind of changes has appeared in the living area of bark beetles?
选项 A、They are moving from the cooler east to the warmer west areas.
B、They have become able to live in the higher areas of the mountains.
C、They are moving from Alaska to Wyoming.
D、They have come to live in the dead trees after wildfires.
答案B
解析 细节题。由文章的最后一段，“Warming is also expanding the beetles’rangeinto higher altitudes．”可知，因为气候变暖，地球上高海拔地区也开始温度升高，这样这种害虫的生活范围向上延展，可以在更大的范围内生活，故B正确。这种扩大是海拔上的，立体的，而不是横向的，故A、C错误。D文中没有提及。
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