[单项选择]Lance Armstrong is thirty-three years old and is one of the best athletes in the world. Scientists say his body operates better than the (47) person. For example, his heart can (48) more than two hundred times a minute. It pumps an extremely large amount of blood and oxygen to his legs. Edward Coyle, head of the Human Performance Laboratory at the University of Texas in Aus tin, tested Armstrong five times from 1992 until 1995. Each time, the cyclist rode a (49) bike for twenty-five minutes with the work rate increasing every five minutes. Scientists measured Armstrong’’s (50) against the amount of oxygen he breathed. Doctor Coyle discovered an 8% increase in Armstrong’’s muscle power. Doctor Coyle (51) Armstrong might have developed more of a certain kind of muscle during his seven years of training. Doctor Coyle also discovered that Armstrong was able to reduce his body weight and body fat before his Tour de France victories. This enabled him to increase his pow