Learningdisabilitiesareverycommon.Theyaffectperhaps10percentofallchildren.Fourtimesasmanyboysasgirlshavelearningdisabilities.Sinceabout1970，newresearchhashelpedbrainscientistsunderstandtheseproblemsbetter.Scientistsnowknowtherearemanydifferentkindsoflearningdisabilitiesandthattheyarecausedbymanydifferentthings.Thereisnolongeranyquestionthatalllearningdisabilitiesresultfromdifferencesinthewaythebrainisorganized.Youcannotlookatachildandtellifheorshehasalearningdisability.Thereisnooutwardsignofthedisorder.Sosomeresearchersbeganlookingatthebrainitselftolearnwhatmightbewrong.Inonestudy，researchersexaminedthebrainofalearning-disabledperson，whohaddiedinanaccident.Theyfoundtwounusualthings.Oneinvolvedcellsintheleftsideofthebrain，whichcontrollanguage.Thesecellsnormallyarewhite.Inthelearning-disabledperson，however，thesecellsweregray.Theresearchersalsofoundthatmanyofthenervecellswerenotinalinethewaytheyshouldhavebeen.Thenervecellsweremixedtogether.ThestudywascarriedoutundertheguidanceofNormanGeschwind，anearlyexpertonlearningdisabilities.DoctorGeschwindproposedthatlearningdisabilitiesresultedmainlyfromproblemsintheleftsideofthebrain.Hebelievedthissideofthebrainfailedtodevelopnormally.Probably，hesaid，nervecellstheredidnotconnectastheyshould.Sothebrainwaslikeanelectricaldeviceinwhichthewireswerecrossed.Otherresearchersdidnotexaminebraintissue.Instead，theymeasuredthebrain’selectricalactivityandmadeamapoftheelectricalsignals.FrankDuffyexperimentedwiththistechniqueatChildren’sHospitalMedicalCenterinBoston.DoctorDuffyfoundlargedifferencesinthebrainactivityofnormalchildrenandthosewithreadingproblems.Thedifferencesappearedthroughouttheebrain.DoctorDuffysaidhisresearchisevidencethatreadingdisabilitiesinvolvedamagetoawideareaofthebrain，notjusttheleftside.1.Scientistsfoundthatthebraincellsofalearning-disabledpersondifferfromthoseofanormalpersonin.A.structureandfunctionB.colorandfunctionC.sizeandarrangementD.colorandarrangement2.WhichofthefollowingisNOTmentionedinthepassage？A.