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】