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There’s more evidence that what’s good for your heart is good for your head．A new study shows that people who run，swim or do other moderate intensity(中等强度的)exercise have brains that look，on average，10 years younger than the brains of couch potatoes． “Our study showed that for older people，getting moderate intensity exercise may be protective，helping them keep their brains work better，”said Dr．Clinton Wright of the University．Of Miami，who led the study．But it’s not necessarily easy．Walking，golf，bowling and yoga didn’t count，and people 从2005个编号中抽取20个号码入样,若采用系统抽样的方法，则抽样的间隔为