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阅读下列文章，选出题的最佳答案：Most young people enjoy physical activities，walking，cycling，football，or mountaineering．
These who have a passion＿21＿climbing high and difficult mountains are often_22_ with astonishment why are men and women_23_to suffer cold and hardship，and to_24_on high mountains? This astonishment is caused，probably，by the difference between mountaineering and other forms of activities_25_ which men give their leisure．
There are no man—made rules，as there are for_26_ games as golf and football．There are，of course，rules of different kinds which it would be dangerous to_27_，but it is this freedom from man-made rules_28_makes mountaineering attractive to many people．Those who climb mountains fire free to use their own_29_．
If we_30_mountaineering with other more familiar sports，we might think that one big difference is_31_ mountaineering is not a “team work”．However，it is only our misunderstanding．There are，in fact，no“matches”_32_ “teams” of climbers，but when climbers are on a rock face linked by a rope on which their lives may _33_，0bviously，there is teamwork．
A mountain climber knows that he may have to fight with natural_34_ that are stronger and more powerful than man．His sport requires high mental and_35_ qualities．
A mountain climber_36_to improve on skill year after year．A skier is probably past his best by the age of thirty，and most international champions_37_in their early twenties．But it is not_38_for men of fifty or sixty to climb the highest mountains in the Alps．They may take more_39_ than younger men，but they probably climb with more skill and less_40_of effort，and they certainly experience equal enjoyment．
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