In Europe, schoolchildren devote time during each school day to calisthenics. North American schools rarely offer a daily calisthenics program. Tests prove that North American children are weaker, slower, and shorter-winded than European children. We must conclude that North American children can be made physically fit only if they participate in school calisthenics on a daily basis. Which one of the following is assumed in the passage? ["School calisthenics are an indispensable factor in European children's superior physical fitness.", 'All children can be made physically fit by daily calisthenics.', 'Superior physical fitness produces superior health.', 'North American children can learn to eat a more nutritious diet as well as to exercise daily.']