Therearetwofactorswhichdetermineanindividual'sintelligence．Thefirstisthesortofbrainheisbornwith．Humanbrainsdifferconsiderably,somebeingmorecapablethanothers．Butnomatterhowgoodabrainhehastobeginwith,anindividualwillhavealoworderofintelligenceunlesshehasopportunitiestolearn．Sothesecondfactoriswhathappenstotheindividual--thesortofenvironmentinwhichheisbroughtup．Ifanindividualishandicappedenvironmentally,itislikelythathisbrainwillfailtodevelopandhewillneverattainthelevelofintelligenceofwhichheiscapable． Theimportanceofenvironmentindetermininganindividual'sintelligencecanbe? demonstratedbythecasehistoryoftheidenticaltwins,PeterandMark．Beingidentical,thetwinshadidenticalbrainsatbirth,andtheirgrowthprocesseswerethesame．Whenthetwinswerethreemonthsold,theirparentsdied,andtheywereplacedinseparatefosterhomes．Peterwasraisedbyparentsoflowintelligenceinanisolatedcommunitywithpooreducationalopportunities．Markwasrearedinthehomeofwell-to-doparentswhohadbeentocollege．Hewasreadtoasachild,senttogoodschools,andgiveneveryopportunitytobestimulatedintellectually．Thisenvironmentaldifferencecontinueduntilthetwinswereintheirlateteens,whentheyweregiventeststomeasuretheirintelligence．Mark'sLQ．was125,twenty-fivepointshigherthantheaverageandfullyfortypointshigherthanhisidenticalbrother．Givenequalopportunities,thetwins,havingidenticalbrains,wouldhavetestedatroughlythesamelevel． ?Thebeststatementofthemainideaofthispassageisthat__________．
A.human brains differ considerably
B.the brain a person is born with is important in determining his intelligence
C.environment is crucial in determining a person's intelligence
D.persons having identical brains will have roughly the same intelligence
正确答案是C