A．从下列单词中选择适当的词填空，每个词只能用一次. Public schools raise cash by selling

A．从下列单词中选择适当的词填空，每个词只能用一次. Public schools raise cash by selling their students everything from biscuits to soft drinks. This contributes　　 51 　　 America's childhood overweight problem. The proportion of overweight 　　 52 　　in the United States more than doubled between 1980 and 2004. For adolescents, that number has more than tripled, In 　　 53 　　 , Congress commissioned a study to examine the snacks sold outside the federally regulated school lunch program. The aim　　 54 　　 to produce sensible recommendations on what schools should-and should not-offer, The Institute of Medicine responded with 　　 55 　　 sure to upset the average soda-drinking high-schooler. The institute's experts created 　　 56 　　 tiers of snack foods that schools might sell instead of junk. The first contains 　　 57 　　such as fruits, vegetables, non-fat yogurt and whole-grain chips. These should be 　　 58 　　to all students any time during the school day. Less nutritious-but not unhealthful-snacks such as 　　 59 　　 potato chips and diet soft drinks are in the second category,　　 60 　　high school students only ought to be able to purchase after school. Sure, students can always bring junk food from home._________