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  3. All competitive ski and snowboarding events now take place largely on man-made snow. Unlike its natural counterpart, the machine

All competitive ski and snowboarding events now take place largely on man-made snow. Unlike its natural counterpart, the machine

admin2013-07-20  26
问题     All competitive ski and snowboarding events now take place largely on man-made snow. Unlike its natural counterpart, the machine-made white stuff can be carefully tweaked to make a more durable and consistent surface: one perfect for record-breaking attempts. Snow-making equipment is viewed as essential in most ski areas to guarantee coverage throughout the season. Nowadays, "natural snow is a bonus," says Rich Brown of snow-making technology company York Snow in Victor, New York.
    The snow "cannons" or "guns" that manufacture snow mimic the natural formation of snowflakes. Snow machines typically force pressurized water through a nozzle (喷嘴), breaking it into a mist of tiny droplets, and then use compressed air or fans to blast them into the air. As the droplets cool, the molecules line, and crystallize into ice particles. The art to snow-making is adjusting the water and air to ensure that the water drops are small enough and sent far enough that they will freeze before they hit the ground. If the air temperature is quite high, for example, dropping the water content and upping the air would create smaller particles that are more likely to freeze. Snow-making machines also frequently incorporate nucleating agents (成核剂)in the water： small quantities of materials such as bacterial protein, on to which the water molecules attach and freeze. By triggering freezing, these agents raise the temperature at which snow can be made.
    Many resorts now use sophisticated computer systems that automatically adjust the air and water output from snow machines based on air temperature, humidity and wind, says Brown. For race courses, experts adjust man-made snow to create a tough, fast and icy course rather than a powdery one. A ski course is also heavily groomed and often intentionally flooded to create patches of ice； these factors generally determine the speed of a race.
    Snow manufacturing is in great demand. Some predict that the need for snow will rocket with, the warming effects of climate change, which are already pushing snow lines up the Alps. But this comes with environmental costs, says Michel Revaz, of the International Commission for Protection of the Alps (ICPRA). Making snow chews up energy and water, and can rob rivers and creeks in the surrounding ecosystems. One way to conserve the mountain environment, Revaz says, would be to reuse winter sports competition facilities rather than building new ones.
The mechanism of snow machines imitates______.
选项
答案the natural formation of snowflakes
解析 同义转述题。本题考查制造人造雪的机械原理。定位句指出，雪炮(枪)是模仿了雪花形成的自然原理。题干中的imitates是原文mimic的同义转述；而snow machines指原文中的snow“canons”or“guns”，故答案为the natural formation of snowflakes。
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