单选题
Every animal is a living radiator--heat formed in its cells is given off through its skin. Warm blooded animals maintain a steady temperature by constantly replacing lost surface heat; smaller animals, which have more skin for every ounce of body weight, must produce heat faster than bigger ones. Because smaller animals burn fuel faster, scientists say they live faster. The speed at which an animal lives is determined by measuring the rate at which it uses oxy gen. A chicken, for example, uses one-half cubit centimeter of oxygen every hour for each gram it weights. The tiny shrew uses four cubit centimeters of oxygen every hour for each gram it weights. Because it uses oxygen eight times as fast, it is said that the mouse-like shrew is living eight times as fast as the chicken. The smallest of the warm-blooded creatures, tile humming-bird, lives a hundred times as fast as an elephant. There is a limit to how small a warm-blooded animal can be. A mammal or bird that weighted only two and a half grams would starve to death, h would bum up its food too rapidly and would not be able to eat fast enough to supply more fuel.
单选题
The selection says that every animal is a living radiator because it ______. A. produces heat in its body cells B. burns fuel to produce heat C. gives off heat through its skin D. requires oxygen to produces heat
【正确答案】
C
【答案解析】第一段第一句话解释了为什么every animal is a living radiator，是因为heat formed in its cells is given off through its skin，即细胞内产生的热量通过皮肤散发出去。
单选题
Warm-blooded animals maintain a steady temperature by ______. A. storing heat in their body cells B. regulating the amount of heat produced C. regulating the amount of heat given off D. constantly replacing lost surface heart
【正确答案】
D
【答案解析】第一段明确指出恒温动物通过constantly replacing lost surface heat来保持体温。
单选题
Small animals are said to live faster than big ones because they ______. A. have more skin for every ounce of body weight B. replace lost heat faster C. bum fuel faster D. maintain a higher body temperature
【正确答案】
C
【答案解析】第一段提到smaller animals．．．must produce beat faster than bigger ones，because smaller animals burn fuel faster，scientists say they live faster，因此可以得出小动物比体积大的动物live faster是因为它们burn fuel faster。
单选题
The speed at which an animal lives is determined by measuring ______. A. the amount of food it eats B. its body temperature C. the rate at which it uses oxygen D. the amount of oxygen it uses
【正确答案】
C
【答案解析】第二段明确指出The speed at which an animal lives is determined by measuring the rate at which it uses oxygen，因此可以直接得出答案。
单选题
An animal weighing less than 2.5 grams would starve because it would not be able to ______. A. get enough oxygen B. maintain its body temperature C. bum its food fast enough D. eat fast enough to supply fuel
【正确答案】
D
【答案解析】文章最后一段指出体重不足2.5克的动物会饿死，是因为它们burn up its food too rapidly and would not be able to eat fast enough to supply more fuel。