题目内容：
ExerciseWhether or not exercise adds to the length of life，it is common experience that a certain amount of regular exercise______(51)health and contributes a feeling of well-being．
Furthermore，exercise______(52)involves play and recreation(娱乐)，and relieves nervous tension and mental fatigue in So_____(53)，is not only pleasant but beneficial．
How much and what kind of exercise one should____(54)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____ (55)of exhaustion but recover promptly with a period of rest．But not so with those off middle age and beyond．For them moderation is(56)vital importance．
Just how much exercise a person of a given age can safely take is a question hard to____(57)．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______(58)for exercise depends on the condition of the heart，the condition of the muscles，the______(59)of exercise，and the regularity with which it is taken．Two general suggestions，however，will____(60)as sound advice for anyone．The first is that the____(61)of the heart and general health should be determined periodically by careful，thorough physical examinations． The other is that exercise should be kept____(62)the point of physical exhaustion．
What type of exercise one should____(63)depends upon one’s physical condition． Young people Can safely enjoy competitive sports，but most older persons do better to limit themselves to less strenuous____(64)．Walking，swimming and skating are among the spots that one Can enjoy and safely____(65) in throughout life．Regularity is important if one is to get the most enjoyment and benefit out of exercise．
根据以上内容，回答题。
A．improves
B．damages
C．enjoys
D．provides
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答案解析：