题目内容：
根据以下资料，回答题。Eatingtoomuchfattyfood,exercisingtoolittleandsmokingcanraiseyourfutureriskofheartdisease.Butthereisanotherfactorthatcancauseyourheartproblemsmoreimmediately:theairyoubreathe.Previousstudieshavelinkedhighexposure(暴露）toenvironmentalpollutiontoanincreasedriskofheartproblem,buttwoanalysesnowshowthatpoorairqualitycanleadtoheartattackorstroke(中风）withinaslittleasafewhoursafterexposure.Inonereviewoftheresearch,scientistsfoundthatpeopleexposedtohighlevelsofpollutants(污染物）wereupto5%morelikelytosufferaheartattackwithindaysofexposurethanthosewithlowerexposure.AseparatestudyofstrokepatientsshowedthatevenairthattheU.S.EnvironmentalProtectionAgency(EPA)considerstobeof“moderate”(良好）qualityandrelativelysafeforourhealthcanraisetheriskofstrokeasmuchas34%within12to14hoursofexposure.
Theauthorsofbothstudiesstressthattheserisksarerelativelysmallforhealthypeopleandcertainlymodestcomparedwithotherriskfactorssuchassmokingandhighbloodpressure.However,itisimportanttobeawareofthesedangersbecauseeveryoneisexposedtoairpollutionregardlessoflifestylechoices.SostricterregulationbytheEPAofpollutantsmaynotonlyimproveenvironmentalairqualitybutcouldalsobecomenecessarytoprotectpublichealth.Thetextmainlydiscussestherelationshipbetween. A．heartproblemsandairquality
B．heartproblemsandexercising
C．heartproblemsandsmoking
D．heartproblemsandfattyfood
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