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  3. Bears mostly live alone, except for mothers and their babies, and males and females during mating season. Bears form temporary g

Bears mostly live alone, except for mothers and their babies, and males and females during mating season. Bears form temporary g

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问题     Bears mostly live alone, except for mothers and their babies, and males and females during mating season. Bears form temporary groups only in exceptional circumstances, when food is plentiful in a small areA. Recent evidence also suggests that giant pandas may form small social groups, perhaps because bamboo is more concentrated than the patchy food resources of other bear species. Other bears may live alone but exist in a social network. A male and female may live in an area partly shared in common—although they tolerate each other, each defends, its range from other bears of the same sex. Male young usually leave their mothers to live in other areas, but female young often live in a range that is commonly shared with that of their mother.
    The key to a bear’s survival is finding enough food to satisfy the energy demands of its large size. Bears travel over huge territories in search of food, and they remember the details of the landscape they cover. They use their excellent memories to return to locations where they have had success finding food in past years or seasons. Most bears are able to climb trees to chase small animals or gain access to additional plant vegetation. The exceptions are polar bears and large adult brown bears—their heavy weight makes it difficult for them to climb trees.
    Bears that live in regions with cold winters spend the coldest part of the year asleep in sheltered dens, including brown bears, American and Asiatic black bears, and female polar bears. Pregnant females give birth in the winter in the protected surroundings of these dens. After fattening up during the summer and fall when food is abundant, the bears go into this winter home to conserve energy during the part of the year when food is scarce. Winter sleep differs from hibernation (冬眠) in that a bear is easily aroused from sleep. In addition, a bear’s body temperature drops only a few degrees in its winter sleep. In contrast, a true hibernator undergoes more extensive changes in bodily functions. For instance, the body temperature of the Arctic ground squirrel drops from 38℃ to as low as -3℃.
Bears sleep in their sheltered dens in cold winter because______.
选项 A、their babies need to be born in a cold and protected surrounding
B、they need to fatten themselves up in the cold season
C、they need to convert their fat into energy in winter
D、they cannot find enough food in the cold season
答案C
解析 从第三段第三句可知，熊在严冬睡眠是因为它们需要把脂肪转化为能量。
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