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阅读理解Even though one out of three American children live within a mileof their school, almost not half of those students often bike or walk to class,scientists report. Children who live in the South, in country areas, or who havecollege-educated parents, are among those least likely to bike or walk toschool, notes the report, which is published in July. Sarah Martin and her workmates at the US Centers for DiseaseControl and Prevention (CDC) studied materials from more than 7, 000 childrenbetween 9 and 15 years of age. They found that almost 35 percent of the children lived within onemil（2010?江苏一模）以黄铁矿为原料制硫酸产生的硫酸渣中含Fe2O3、SiO2、Al2O3、CaO、MgO等．现以硫酸渣制备铁红（Fe2O3）的过程如下：（1）酸溶过程中Fe2O3与稀硫酸反应的化学方程式是Fe2O3+3H2SO4=Fe2（SO4）3+3H2OFe2O3+3H2SO4=Fe2（SO4）3+3H2O．（2）还原过程中加入FeS2是将溶液中的Fe3+还原为Fe2+，而本身被氧化为SO 2-4，写出有关的离子方程式：FeS2+14Fe3++8H2O=15Fe2++2SO42-+16H+FeS2+14Fe3++8H2O=15Fe2++2SO42-+16H+．（3）氧化过程中通入空气和加入NaOH是为了将溶液中的铁元素充分转化为沉淀而析出，写出有关的离子方程式：4Fe2++O2+2H2O+8OH-=4Fe（OH）3↓4Fe2++O2+2H2O+8OH-=4Fe（OH）3↓．（4）生产过程中，为了确保铁红的质量，氧化过程需要调节溶液的pH至3～4，其目的是使Fe3+沉淀完全，而其他金属阳离子不生成沉淀使Fe3+沉淀完全，而其他金属阳离子不生成沉淀．