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Cells cannot remain alive outside certain limits of temperature, and much narrower limits mark the boundaries of effective funct
Cells cannot remain alive outside certain limits of temperature, and much narrower limits mark the boundaries of effective funct
admin
2012-07-22
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】______ .
【C5】
选项
A、they
B、it
C、we
D、what
答案
B
解析
it作形式主语。
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0
专业英语四级
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