[单项选择]America is a country on the move. In unheard of numbers, people of all ages are exercising their way to better health. According to the latest figures, 59 percent of American adults exercise regularly-up 12 percent from just two years ago and more than double the figure of 25 years ago. Even non-exercisers believe they would be more attractive and confident if they were more active.
It is hard not to get the message. The virtues of physical fitness are shown on magazine covers, postage stamps, and television ads for everything from beauty soaps to travel books. Exercise as a part of daily life did not catch on until the late 1960s when research by military doctors began to show the health benefits of doing regular physical exercises. Growing publicity (宣传) for races held in American cities helped fuel a strong interest in the ancient sport of running. Although running has leveled off in recent years as Americans have discovered equally rewarding and sometimes safer forms of
A. are yet to be proved
B. are to be further studied
C. are supported by scientific evidence
D. are self-evident