A、Studying yoga. B、Adult education. C、Playing tennis. D、The search for physical fitness. B细节题。文中明确提到adult education是自我改善的另一种形式。

In America, self-improvement is a national pastime. Every year, more and more Americans spend their leisure time trying to improve themselves one way or another.
    One popular form of self-improvement is the search for physical fitness. Thousands of Americans who never exercised are now out on the streets jogging in fashionable running suits and expensive sneakers. They boast of how many miles they run each day and of how many pounds they lose each week. Others are turning to swimming, tennis, dance, and the martial arts to improve their physical fitness.
    Instead of running around the park in the morning or evening, other Americans are studying yoga or are meditating quietly in their homes. They are seeking to improve themselves by finding peace and tranquility.
    Adult education is another form of self-improvement. After a hard day’s work, many Americans take evening courses at a local high school or college. There they can study a variety of subjects. Often these people are preparing to return to the job market or trying to qualify themselves for better jobs. A mother busy raising her children might attend night school to learn secretarial skills. A secretary might return to study accounting. Some retired people go back for the education they missed at an earlier age.
Questions 19 to 21 are based on the passage you have just heard.
19. What’s the second form of self-improvement mentioned by the speaker?
20. Where do many Americans go for adult education?
21. Why do some retired people go back for education?