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  3. Cells cannot remain alive outside certain limits of temperature and much narrower limits mark the boundaries of effective func

Cells cannot remain alive outside certain limits of temperature and much narrower limits mark the boundaries of effective func

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问题     Cells cannot remain alive outside certain limits of
temperature and much narrower limits mark the boundaries of
effective functioning. Enzyme systems of mammals and birds are
most efficient only with a narrow range around 37℃; a departure【M1】______
of a few degrees from this value serious impairs their functioning.【M2】______
Even though cells can survive wider fluctuations the integrated
actions of bodily systems are impaired. Other animals have a wide【M3】______
tolerance for changes of bodily temperature.
    For century it has been recognized that mammals and birds【M4】______
differ other animals in the way they regulate body temperature.【M5】______
Ways of characterizing the difference have become more accurate
and meaningful over time, but popular terminology still reflects an【M6】______
old division into " warm-blooded" and " cold-blooded" species;
warm-blooded included mammals and birds whereas all other
creatures were considered cold-blooded. As more species were
studied, it became evident that this classification was adequate. A【M7】______
cold-blooded fence lizard usually has a body temperature only a
degree or two below those of humans and so is not cold. Therefore【M8】______
the next distinction was taken between animals that maintain a【M9】______
constant body temperature, called homeotherms, and those whose
body temperature varies with their environments, called
poikilotherms. But this classification was also proved inadequate,【M10】______
because among mammals there are many that vary their body
temperatures during hibernation. Furthermore, many invertebrates
that live in the depths of the ocean never experience change in the
depths of the ocean, and their body temperatures remain constant.
【M6】
选项
答案an—the
解析 词汇错误。此处是特指过去对动物的一种划分方法，即把动物划分为暖血动物和冷血动物，故应用定冠词。
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