Achildwhohasoncebeenpleasedwithatalelikes,asarule,tohaveitretoldinalmostthesamewords,butthisshouldnotleadparentstotreatprintedfairystoriesasformaltexts.Itisalwaysmuchbettertotellastorythanreaditoutofabook,and,ifaparentcanproducewhat,intheactualsituationofthetimeandthechild,isanimprovementontheprintedtext,somuchthebetter.Achargemadeagainstfairytalesisthattheyharmthechildbyfrighteninghimormakinghimsadthinking.Toprovethelatter,onewouldhavetoshowinacontrolledexperimentthatchildrenwhohavereadfairystoriesweremoreoftensorryforcrueltythanthosewhohadnot.Astofears,thereare,Ithink,somecasesofchildrenbeingdangerouslyterrifiedbysomefairystory.Often,however,thisarises(出现)fromthechildhavingheardthestoryonce.Familiaritywiththestorybyrepetitionturnsthepainoffearintothepleasureofafearfacedandmastered.Therearealsopeoplewhoobjecttofairystoriesonthegroundsthattheyarenotobjectivelytrue,thatgiants,witches,two-headeddragons,magiccarpets,etc.donotexist;andthat,insteadofbeingfondofthestrangesideinfairytales,thechildshouldbetaughttolearntherealitybystudyinghistory.Ifindsuchpeople,Imustsaysopeculiar(奇怪的)thatIdonotknowhowtoarguewiththem.Iftheircaseweresound,theworldshouldbefullofmadmenattemptingtoflyfromNewYorktoPhiladelphiaonastickorcoveringatelephonewithkissesinthebeliefthatitwastheirbelovedgirl-friend.Nofairystoryeverdeclaredtobeadescriptionoftherealworldandnocleverchildhaseverbelievedthatitwas.1.Theauthorconsidersthatafairystoryismoreeffectivewhenitis_______.
python3解释器执行{1,2,'a'}|{2,3,4}的结果为():A{2,3,4}B{1,2,3,4,'a'}C{1,2,3,4}D{2,3,4,'a'}