题目内容：
阅读下文，回答题。Exercise
Whether or not exercise adds to the length of life，it is common experience that a certain amount of regular exercise___1___health and contributes a feeling of well-being．
Furthermore，exercise___2___involves play and recreation(娱乐)，and refieves nervous tension and mental fatigue in So__3___，is not only pleasant but beneficial．
How much and what kind of exercise one should__4 _merits careful consideration．
The growing child and the normal young man and young woman thrill(兴奋)with the
exhilaration of strenuous sports．They fatigue to the__5__ of exhaustion but recover promptly with a period of rest．But not SO with those offlniddle age and beyond．For them moderation is 6 vital importance．
Just how much exercise a person of a given age can safely take is a question hard to__7__．Individual variability is too great to permit generalization．A game of tennis may be perfectly safe for one person of forty but folly(愚蠢)for another．The safe___8___for exercise depends on the condition of the heart，the condition of the muscles，the___9___of exercise，and the regularity with which it is taken．Two general suggestions，however，will__10__as sound advice for anyone．The first is that the 11___of the heart and general health should be determined periodically by careful，thorough physical examinations．
The other is that exercise should be kept__12__the point of physical exhaustion．
What type of exercise one should___13_ depends upon one’s physical condition．
Young people Can safely enjoy competitive sports，but most older persons do better to limit themselves to less sWenuous__14__．Walking，swimming and skating are among the spots that one Can enjoy and safely__15__ in throughout life．Regularity is i—mportant if one is to get the most enjoyment and benefit out of exercise．
请在1处填写正确答案。 A．improves
B．damages
C．enjoys
D．provides
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