题目内容：
根据以下材料回答题 Inthepast,theParkServicefocusedonmakingthebigscenicparksmore21andcomfort-ablefortourists.Roadswerepavedtoallow"windshieldvisitors"toexperiencethegrandeurofna-turewithoutleavingtheircars,anda22numberofhotelsandgrocerystoreswerepermittedtoopen23theparkboundaries.
Nowthistrendischanging.Planshavebeenmadeto24theparkstotheirnaturalconditionasmuchaspossible.Theobjectiveofsuchamovewouldbetosecurethepreservationoftheparksforfuturegenerations,25allowingpresent-dayvisitorstoexperiencepurewilderness,26fromanyobvioussignsofcivilization--anopportunitywhichisquicklydisappearinginthetwenti-ethcentury.27planscallonly28areductioninthenumberofcars29intotheparkseachday,but30,touristsmayhavetoleavetheircarsatthegatesandtheneithervisittheparkonfoot31usepark3233,storesandhotelsmaynolongerbeallowedwithinparkboundariesandeventhenumberofcampgroundsmayberestricted.
DenaliNationalParkinAlaskaservesasanexcellent34forthisnewtypeofpark,onewhichhasbeenchangedonlyslightlyfromits35state.Thereisonlyoneroad,unpavedin36,whichcross37Denali.Ascartrafficisstrictlylimited,manyvisitorsexperiencethemagnificent38andwildlifefromaparkbus.Therearenohotelsorstoresandonlysevencamp-groundswithinDenali's3,006squaremiles.This39isolationoffersbackpackers,canoeists,andothersportenthusiastsa40.physicalandpsychologicalchallenge.
第21题应选 A．possible
B．accessible
C．approachable
D．reachable
参考答案：
答案解析：