单项选择题

Large animals that inhabit the desert have evolved a number of adaptations for reducing the effects of extreme heat. (31) adaptation is to be light in color, and to (32) rather than absorb the sun’s rays. Desert mammals also depart from the normal mammalian practice of maintaining a (33) body temperature. (34) trying to keep down the body temperature deep inside the body, (35) would involve the expenditure of water and energy, desert mammals allow their temperatures to rise to what would normally be fever (36) , and temperatures as high as 46 degrees Celsius have been measured in gazelles (瞪羚羊).
Another strategy (37) large desert animals is to tolerate the loss of body water to a point (38) would be fatal for non-adapted animals. The camel can lose up to 30 percent of its body weight (39) water without harm to itseff, (40) human beings die after losing only 12 to 13 percent oftheir body weight. An equally important adaptation is the ability to (41) this water loss (42) onedrink. Desert animals can drink prodigious volumes in a short time, and camels have been known to (43) over 100 liters in a few minutes. A very dehydrated person, (44) , cannot drink enoughwater to rehydrate at one (45) , because the human stomach is not sufficiently big and because a toorapid (46) of the body fluids causes death from water intoxication. The (47) of water loss is ofobvious advantage in the desert, as animals do not have to remain (48) a water hole but can obtain food from gazing sparse and far-flung pastures. Desert-adapted mammals have the (49) ability to feednormally when extremely dehydrated; it is a common experience in people that appetite is lost even (50) conditions of moderate thirst.