题目内容：
根据以下材料，回答题Moods,saytheexperts,arefeelingsthatarelikelytobecomefixed,havingeffectsonone'sout-look(wayoflookingatthings)forhours,daysorevenweeks.That'sgreatifyourmoodisapleasantone,butaproblemifyouaresad,anxious,angryorsimplylonely.
Perhapsthebestwaytodealwithsuchmoodsistotalkthemout;sometimes,though,thereisnoonetolisten.Modernpharmacology(药物学)offersalottranquilizers(镇定剂)andanti-anxietydrugs.Whatmanypeopledon'trealize,however,isthatscientistshavediscoveredtheeffectivenessofseveralnon-drugmethodstomakeyoufreefromanunwantedmood.Thesecanbejustasusefulasdrugs,andhavetheaddedbenefitofbeingnonpoisonous.Sonexttimeyoufeeloutofsorts,don'theadfor
thedrugstore--trythefollowingmethod.
Ofallthemood-changingself-helptechniques,aerobicexerciseseemstobethebestcureforabadmood."Ifyoucouldkeeptheexercise,you'dbeinhighspirits,"saysKathrynLance,authorofRunningforHealthandBeauty.
Researchershaveexplainedbiochemicalandvariousotherchangesthatmakeexercisecomparefavorablytodrugsasmood-raiser.Physicalworksuchashousework,however,doeslittle.Thekeyisaerobicexercise--running,cycling,walking,swimming,orotherrepetitiveandsustainedactivitiesthatincreasetheheartrateandcirculation(循环),andimprovethebody'suseofoxygen.Dothem"foratleast20minutesatime,threetofivetimesaweek.
Whatisthemainsubjectofthepassage? A．Howtobeatabadmood.
B．Howtotalkbadmoodsout.
C．Howtodophysicalexercises.
D．Howtodoaerobicexercise.
参考答案：
答案解析：