题目内容：
Questionsarebasedonthefollowingpassage:
AllovertheworldmentionoftheBritisheducationsuggestsapictureofthe"publicschool",anditsuggestsinparticularthenamesofcertainveryfamousinstitutions--Eton,OxfordandCambridge;butpeopledonotalwaysrealizewhatplacethesesituationsoccupyinthewholeeducationalsystem．OxfordandCambridgeareuniversitieseachhavingabout12,000studentsoutofatotalofover250,000studentsatallBritishuniversities.(54)Etonisapublicschool,andthebestknownofthepublicschools,whichtinspiteoftheirnames,arenotreallypublicatall,butindependentandprivatesecondaryschoolstakingboysfromtheageofthirteentoeighteen．ThepublicschoolsinrealityformaverysmallpartoftheschoolsystemofsecondaryeducationofGreatBritain;onlyaboutoneoutoffortyEnglishboysgoestoapublicschool,andoneoutof1500toEton.
(55)Apartfromtheso-calledpublicschoolsthereisacompletesystemofstateprimaryandsecondaryeducation,whichresemblesinitsgeneralformthestateeducationinmostothercountries.
Allchildrenmust,bylaw,receivefull-timeeducationbetweentheagesoffiveandsixteen．Anychildmayattend,withoutpayingfees,aschoolprovidedbythepublicauthorities,andthegreatmajorityattendsuchschools．Theymaycontinue,stillwithoutpayingfees,untiltheyareeighteen.
Thepublicschools,althoughunimportantnumerically,havebeenEngland'smostpeculiarandcharacteristictoeducationalmethods,andtheyhaveanimmenseinfluenceonthewholeofEnglisheducationalpracticeandontheEnglishsocialstructure.
Whatwasthepurposeoftheauthortowritethepassage? A．ItwastotellpeoplethedifferencebetweenEtonontheonehandandOxfordandCambridgeontheother
B．ItwastotellpeoplewhatthepublicschoolsinGreatBritainarelike
C．ItwastotellpeoplesomethingaboutBritaineducationalsystem
D．Alloftheabove
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