Today,asineveryotherdayoftheyear,morethan3000U.S.adlescentswillsmoketheirfirstcigaretteontheirwaytobecomingregularsmokersasadults.Duringtheirlifetime,itcanbeexpectedthatofthese3000about23willbemurdered,30willdieintrafficaccidents,andnearly750willbekilledbyasmoking-relateddisease.Thenumberofdeathsattributedtocigarettesmokingoutweithtsallotherfactors,whethervoluntaryorinvoluntary,asacauseofdeath. Sincethelate1970s,whendailysmokingamonghighschoolseniorsreached30precent,smokingratesamongyouthhavedeclined.Whilethedeclineisimpressive,severalimportantissuesmustberaised. First,inthepastseveralyears,smokingratesamongyouthhavedeclinedverylittle.Second,inthelate1970s,smokingamongmalehighschoolseniorsexceededthatamongfemalebynearly10percent.Thestatisticisreversing.Third,severalrecentstudieshaveindicatehighschooldropoutshaveexcessivelyhighsmokingrates,asmuchas75percent. Finally,thouthsignificantdeclinesinadolescentsmokinghaveoccurredinthepastdecade,nodefinitereasonsforthedeclineexist.Withinthiscontext,theNaionalCancerInstiute(NCI)beganitscurrentefforttodeterminethemosteffecivemeasurestoreducesmokingleveslamongyouth. Accordingtotheauthor,thedeathsamongyoutharemainlycausedby_____.
A.a.traffic accidents B.b.smoking-related desease C.c.murder D.d.all of these正确答案B
