Every animal is a living radiator-heat formed in its cells is given 【M1】______
through its skin. Warm-blooded animals maintain a steady temperature
by constantly replacement lost surface heat; similar animals, which have more 【M2】______
skin for every ounce of body weight, must produce heat faster than bigger
one. Because smaller animals burn fuel faster, scientists say they live faster. 【M3】______
The speed by which an animal lives is determined by measuring the rate at 【M4】______
which it uses oxygen. A chicken, for example, uses one-half cube centimeter 【M5】______
of oxygen every hour for each gram it weighs. The tiny shrew uses four cubic
centimeters of oxygen every hour for each gram it weighs. Because of it uses 【M6】______
oxygen eight times as fast, it was said that the mouselike shrew is living eight 【M7】______
times as fast as the chicken. The smallest of the warm-blooded creatures, the
humming bird, lives a hundred times as fast as an elephant.
There is no limit to how small a warm-blooded animal can be. A mammal or 【M8】______
bird that weighed only two and a half grams would starve to dead. It would 【M9】______
burn up its food too rapidly and would not be able to eat faster enough to supply 【M10】______
more fuel.
【M1】

A.
B.
【M1】