For centuries it has been recognized that mammals and birds differ from other animals in the way they regulate body temperature. Ways of【C1】________the difference have become more accurate and meaningful over time, but popular terminology still reflects the old【C2】________into "warm blooded" and "cold blooded" species; warm blooded included mammals and birds,【C3】________all other creatures were considered cold blooded. As more species were studied, it became evident that this classification was【C4】________. A fence lizard usually has a body temperature only a degree or two below that of humans and so is not cold. Therefore the next distinction was made between animals that maintain a【C5】________body temperature and those whose body temperature varies with their environment. But this classification also【C6】________inadequate, because among mammals there are many that vary their body temperatures during hibernation. Furthermore, many invertebrates that live in the【C7】________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 regulated chiefly by internal metabolic processes and those whose temperature is regulated by the【C8】________. The latter do so mainly by moving to favorable sites or by changing their exposure to【C9】________sources of heat. Mammals and birds also regulate their temperature by choosing favorable environments, but primarily they regulate their temperature by【C10】________a variety of internal adjustments.
A. division B. sufficient C. constant D. depths E. exterior F. whereas G. stable H. proved I. external J. measuring K. environment L. inadequate M. making N. bottom O. characterizing
【C1】
O
空格位于介词of后面，名词the difference前面，由此判断此处填入动词的现在分词形式。由后半分句中的 “warm blooded”和“cold blooded”的分类可知，此处是要表达随着时间的推移，描绘这种差异的方式越来越准确和有意义。characterizing“描述……的特征”符合题意。本文通篇描述的是以不同的体温调节方式将动物进行分类，没有涉及测量的问题，measuring“测量，度量”不符合语义。
【C2】
A
空格前的the old提示，此处填入名词。由into “warm blooded” and “cold blooded” species可推知，此处填入表示“分类”的名词. division“分类；区分”符合句意。
【C3】
F
空格位于两个句子间。由此判断此处填入连词。此句讲到恒温动物包括哺乳动物和鸟类，……其他的动物被认为是冷血动物。由此推断此处是表达两类动物的对比，表转折的连词whereas“而，却；反之”符合题意。
【C4】
L
空格前的was提示，此处填入动词的过去分词形式或形容词。下文所列举的蜥蜴的例子说明恒温动物和冷血动物的传统分类方式不够恰当。inadequate表示“不充分的，不恰当的”，符合题意。sufficient表示“足够的，充足的”，用在此处不符合语义。
【C5】
C
空格前的a和后面的名词短语表明，此处需要填入修饰body temperature的词。本句讲到人们进一步把动物分为两类，根据本句的关键词varies with“随……而变化”可知此处需要填入一个与之意思相反的词。constant“不变的；始终如一的”符合语义。stable表示状态稳定，此处表达的是“恒定不变”的概念，故排除。
【C6】
H
空格位于名词和形容词之间，推断此处填入系动词。本句说的是这种分类也……不充分。因为很多哺乳动物在冬眠期间体温也是变化的。prove“证明是，显示出”符合语义。
【C7】
D
空格前的the提示，此处填入名词。本句意为：此外，生活在深海区域中的许多无脊椎动物绝不会在刺骨的冷水中体验到温度的变化，它们的体温也会保持恒定。in the depths of the ocean是习惯搭配，意为“在深海区域”。bottom在表示“(海，河，湖) 底。底部”时，与之搭配的介词是at。
【C8】
K
空格前的the提示，此处填入名词。此句讲动物根据体温调节方式不同分成两类，前一类是通过新陈代谢来调节，属于内部调节(internal)，相对的，后一类应该是通过外界来调节，environment“环境”符合语境。
【C9】
I
由空格前的exposure to推断此处填入修饰sources的词。结合前句中的internal“内部的；体内的”可知此处词义应与之相对。external“外面的；外部的”符合语义。exterior“(位于) 外面的；外表的”一般用在非常具体的事物上，最常用来形容房屋、物品的外部等。
【C10】
M
空格前by提示，此处填入动词的现在分词形式。make adjustments“进行调整”为常用搭配，此处表示哺乳动物和鸟类也会通过选择合适的环境来调节体温，但主要还是通过进行一系列内在的调整来调节。