[单选题]Lifeinthetwentiethcenturydemandspreparation.Today,allindividualsinacountrymusthaveadequateschoolingtopreparethemfortheirworkaswellasfortheirresponsibilitiesascitizens.Withthisinmind,nationalleaderseverywhereareplacingmoreemphasisontheeducationoftheyoung.IntheUnitedStates,governmentofficials,parents,andteachersareworkinghardtogivethechildren--tomorrow'sdecisionmakersthebestpreparationavailable.ThereisnonationalschoolpolicyintheUnitedStates.Eachofthefiftystatesmakesitsownrulesandregulationsforitsschools,buttherearemanysimilaritiesamongthefiftyschoolsystems.Publicschoolsinallstatesaresupportedbytaxespaidbythecitizensoftheindividualstate.Inmoststatesthechildrenarerequiredtoattendschooluntiltheyreachtheageofsix.Whentheybecomesixyearsold,childrenbeginelementaryschool.Aftersixyearsinelementaryschool,theygointojuniorhighschoolandremainthereforthreeyears.Thelastthreeyearsoftheirpublicschooleducationarespentinseniorhighschool,fromwhichtheygraduateattheageofeighteen.Agreatnumberofhighschoolgraduatescontinuetheireducationinoneofthemanycollegesoruniversitiesinthecountry.Afterfouryears,theyreceiveaBachelor'sdegree.SomecontinuestudyingforaMaster'sdegreeandperhapsaDoctor’sdegree.AtwhatagedoesachildintheUnitedStatesenterelementaryschool?
