题目内容：
Questionsarebasedonthefollowingpassage. Therearetwofactorswhichdetermineanindividual'sintelligence．Thefirstisthesortofbrainheisbornwith．Humanbrainsdifferconsiderably,somebeingmorecapablethanothers．Butnomatterhowgoodabrainhehastobeginwith,anindividualwillhavealoworderofintelligenceunlesshehasopportunitiestolearn．Sothesecondfactoriswhathappenstotheindividual--thesortofenvironmentinwhichheisreared．Ifanindividualishandicappedenvironmentally,itislikelythathisbrainwillfailtodevelopandhewillneverattainthelevelofintelligenceofwhichheiscapable.
Theimportanceofenvironmentindetermininganindividual'sintelligencecanbcdemonstratedbythecasehistoryoftheidenticaltwins,PeterandMarkX．Beingidentical,thetwinshadidenticalbrainsatbirth,andtheirgrowthprocesseswerethesame．Whenthetwinswerethreemonthsold,theirparentsdied,andtheywereplacedinseparatefosterhomes．Peterwasrearedbyparentsoflowintelligenceinanisolatedcommunitywithpooreducationalopportunities．Markwasrearedinthehomeofwell-to-doparentswhohadbeentocollege．Hewasreadtoasachild,senttogoodschools,andgiveneveryopportunitytobestimulatedintellectually．Thisenvironmentaldifferencecontinueduntilthetwinswereintheirlateteens,whentheyweregiventeststomeasuretheirintelligence．Mark'sI.Q．was125,twenty-fivepointshigherthantheaverageandfullyfortypointshigherthanhisidenticalbrother．Givenequalopportunities,thetwins,havingidenticalbrains,wouldhavetestedatroughlythesamelevel.
Whichofthefollowingisthebesttitleforthepassage? A．MeasuringYourIntelligence.
B．IntelligenceandEnvironment.
C．TheCaseofPeterandMark.
D．HowtheBrainInfluencesIntelligence.
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