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  3. Large animals living in the desert have developed a number of adaptations for reducing the effects of extreme heat. One adaptati

Large animals living in the desert have developed a number of adaptations for reducing the effects of extreme heat. One adaptati

admin2011-03-01  60
问题    Large animals living in the desert have developed 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 animals also depart from other animals’ normal practice of maintaining a constant body temperature. Instead of trying to keep down the body temperature deep inside the body, which would involve the loss of water and energy, large desert animals 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. The over-heated body then cools down during the cold desert night, and indeed the temperature may fall unusually low by dawn, as low as 34 degrees Celsius 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 an 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% of its body weight as water without harm to itself, whereas human beings die after losing only 12%-13% of their body weight. An equally important adaptation is the ability to recover this water loss at one drink. Desert animals can drink massive volumes of water in a short time, and camels have been known to drink over 100 liters in a few minutes. A person who severely loses water, on the other hand, cannot drink enough water for recovery at one session, because the human stomach is not sufficiently big and because a too rapid mixing of the body liquid with water causes death from water intoxication. The tolerance of water loss is of obvious advantage in the desert, as animals do not have to remain near a water hole but can obtain food by searching quite a few distant places. Desert-adapted animals have the further ability to feed normally when extremely thirsty: it is a common experience in people that appetite is lost even under conditions of moderate thirst.
What does the passage mainly discuss?
选项 A、How large desert animals adapt to the environment.
B、Weather conditions in the desert.
C、Human use of large desert animals.
D、Health problems of large desert animals.
答案A
解析 主旨理解题。第一段第一句话告诉我们本篇主要是描述生活在沙漠里的大型动物在进化过程中所形成的种种适应沙漠环境的生理特征和生活习性。然后，在后面的二段文字中逐项说明这些生理特征和生活习性。
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