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

admin2012-07-22  65
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 within a narrow 【C1】______ around 37℃; a 【C2】______  , of a few degrees from this value seriously impairs their functioning. Even though cells can survive wider 【C3】______  , the integrated actions of bodily systems are impaired. Other animals have a wider tolerance 【C4】______  changes of bodily temperature.
     For centuries 【C5】______  has been recognized that mammals and birds differ from other animals in the way they regulate body temperature. Ways of 【C6】______  the difference have become more accurate and meaningful over time, but popular terminology still reflects the old division 【C7】______  " warm blooded" and "cold blood- ed " species; warm blooded included mammals and birds, 【C8】______  all other creatures were considered cold blooded. 【C9】______  more species were studied, it became evident that this classification was 【C10】______  A fence lizard usually has a body temperature only a degree or two below 【C11】______  of humans and so is not cold. 【C12】______  the next distinction was made between animals that maintain a 【C13】______  body temperature and those whose body temperature varies with their environment. But this classification also proved inadequate, 【C14】______  among mammals there are many that vary their body temperatures during hibernation. 【C15】______  many invertebrates that live in the 【C16】______ of the ocean never experience a change in the chill of the deep water, and their body temperatures remain constant. The current distinction is between animals whose body temperature is 【C17】______  chiefly by internal metabolic processes and those whose temperature is regulated by the 【C18】______ . The latter do so mainly by moving to favorable sites or by changing their exposure to 【C19】______  sources of heat. Mammals and birds also regulate their temperature by choosing favorable environments, but primarily they regulate their temperature by making a variety of internal 【C20】______ .
【C12】
选项 A、But
B、However
C、Therefore
D、Meanwhile
答案C
解析 由于前句提出了反例，指出传统的分类有不足之处。本句接着讲到更准确的分类。因此可推断它们之间是因果关系，所以选C。
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专业英语四级

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