A、Those who have heart attacks. B、Those who have the desire to be physically fit. C、Those who have spare time. D、Those who have

In recent years, many Americans of both sexes and various ages have become interested in improving their bodies. They have become devoted to physical fitness.
    Many people have a strong desire to be more physically fit. By nature, Americans are enthusiastic and energetic about hobbies or pastimes.
    Many of them apply this enthusiasm, optimism, and energy to running. As a result, there are running clubs to join and numerous books and magazines to read about running.
    The desire to be physically fit is explained by a "passion" for good health. The high rate of heart attacks in the 1960s caused an increase of interest in improving the human body.
    Middle-aged men especially suffer from heart attacks. Thus, they are one group strongly interested in more physical exercises. In fact, many doctors encourage their patients to become more physically active, especially those who have inactive jobs. It is interesting to note that the rate of heart attacks began to decease between 1972 and 1974 and it is still decreasing. Physical fitness has now become a new "love" of Americans. Will it last long? Only time will tell--or until another "new passion" comes along?