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Cells cannot remain alive outside certain limits of temperature, and much n
Cells cannot remain alive outside certain limits of temperature, and much n
游客
2023-11-15
8
管理
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】______ . [br] 【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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