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  3. Large animals that live in the desert have evolved a number of adaptations for reducing the effects of extreme heat. One adaptat

Large animals that live in the desert have evolved a number of adaptations for reducing the effects of extreme heat. One adaptat

admin2010-09-10  51
问题     Large animals that live in the desert have evolved a number of adaptations for reducing the effects of extreme heat. One adaptation is to be light in color, and to reflect rather than absorb the sun’ s rays. Desert mammals (哺乳动物) also depart from the normal mammalian practice of maintaining a constant body temperature. Instead of trying to keep down the body temperature deep inside the body, which would involve the expenditure of water and energy, desert mammals allow their temperatures to rise to what would normally be fever height, and temperatures as high as 46 degrees Celsius have been measured in Grant’s gazelles (一种小羚羊). The overheated body then cools down during the cold desert night and indeed the temperature may fall unusually low by dawn, as low as 34 degrees in the camel. This is an advantage since the heat of the first few hours of daylight is absorbed in warming up the body and excessive buildup of heat does .not begin until well into the day.
    Another strategy of large desert animals is to tolerate the loss of body water to a point that would be fatal for non-adapted animals. The camel can lose up to 30 percent of its body weight as water with no harm to itself, whereas human beings die after losing only 12 to 13 percent of their body weight. An equally important adaptation is the ability to supply this water loss at one drink. Desert animals can drink great volumes in a short time, and camels have been known to take in over 100 liters in a few minutes. A very dehydrated (脱水) person, on the other hand, can not drink enough water to supply water at one session, because the human stomach is not sufficient big and because a too rapid dilution (稀释) of the body fluid causes death from water intoxication. The tolerance of water loss is of obvious advantage in the desert, as animals don’ t have to remain near a water hole but can obtain food from grazing sparse and far-flung natures. Desert-adapted mammals have the further ability to feed normally when extremely dehydrated: it is a common experience in people that appetite is lost even under conditions of moderate thirst.
What is the main topic of this passage?
选项 A、The evolution of desert animals.
B、The advantages of desert animals.
C、Adaptations of desert animals.
D、Temperature and water in desert animals.
答案C
解析 本题测试文章的中心思想。文章首句为主题句，下文举例说明，如"One adaptation is... Another strategy ...”。[A]太宽，[B]和[D]局限于文中细节，只有[C]符合题意。
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