[单选题]根据以下材料，回答题
Peoplehavesmokedcigarettesforalongtimenow.ThetobaccowhichisusedtomakecigaretteswasfirstgrowninwhatisnowpartoftheUnitedStates.ChristopherColumbus,whodiscoveredAmerica,sawtheIndianssmoking.SoonthedriedleavesweretransportedtoEurope.Inthelate1800s,theTurksmadecigarettespopular.
Cigarettesmokecontainsatleasttwoharmfulsubstances,tarandnicotine.Tar,whichformsasthetobaccoburns,damagesthelungsandthereforeaffectsbreathing.Nicotine,whichisfoundintheleaves,causesthehearttobeatfasterandincreasesthebreathingrate.Nicotineinlargecankillapersonbystoppingaperson′sbreathingmuscles.Smokersusuallytakeinsmallamountsthatthebodycanquicklybreakdown.
Nicotinecanmakenewsmokersfeeldizzy(头晕)orsicktotheirstomachs.Theheartrateforyoungsmokersincreases2to3beatsperminute.Nicotinealsolowersskintemperatureandreducesbloodflowinthelegsandfeet.Itplaysanimportantroleinincreasingsmokers′riskofheartdiseaseandstroke.
Smokingcigarettesisdangerous.Cigarettesmokingwasthecauseoflungcancerandseveralotherdeadlydiseases.
______doesn′tmakeone′sheartbeatasusual.查看材料