阅读理解：请根据短文内容，为每题确定l个最佳选项。ANewStrategytoOvercomeBreastCancer。Post-menopausal（绝经后）womenwhowalkforanhouradaycancuttheirchanceofbreastcancersignificantly,astudyhassuggested.Thereport,whichfollowed73,000womenfor17years,foundwalkingforatleastsevenhoursaweekloweredtheriskofthedisease.TheAmericanCancerSocietyteamsaidthiswasthefirsttimereducedriskwasspecificallylinkedtowalking.UKexpertssaiditwasmoreevidencethatlifestyleinfluencedcancerrisk.ArecentpollforthecharityRamblersaquarterofadultswalkfornomorethananhouraweek,butbeingactiveisknowntoreducetheriskofanumberofcancers.Thisstudy,publishedinCancerEpidemiology,Biomarkers&Prevention,followed73.615womenoutof97,785aged50-74whohadbeenrecruitedbytheAmericanCancerSocietybetween1992and1993,soitcouldmonitortheincidenceofcancerinthegroup.Theywereaskedtocompletequestionnairesontheirhealthandonhowmuchtimetheywereactiveandparticipatinginactivitiessuchaswalking,swimmingandaerobics（有氧运动）andhowmuchtimetheyspentsittingwatchingtelevisionorreading.Theycompletedthesamequestionnairesattwo-yearintervalsbetween1997and2009.Ofthewomen,47%saidwalkingwastheironlyrecreationalactivity.Thosewhowalkedforatleastsevenhoursperweekhada14%lowerriskofbreastcancercomparedtothosewhowalkedthreeorfewerhoursperweek.Dr.AlpaPatel,aseniorepidemiologistattheAmericanCancerSocietyinAtlanta,Georgia,wholedthestudy,said:”Giventhatmorethan60%ofwomenreportsomedailywalking,promotingwalkingasahealthyleisure-timeactivitycouldbeaneffectivestrategyforincreasingphysicalactivityamongstpost-menopausalwomen.Wewerepleasedtofindthatwithoutanyotherrecreationalactivity,justwalkingonehouradaywasassociatedwithalowerriskofbreastcancerinthesewomen.””Morestrenuous（紧张的）andlongeractivitiesloweredtheriskevenmore.”BaronessDelythMorgan,chiefexecutiveofBreastCancerCampaign,said:”Thisstudyaddsfurtherevidencethatourlifestylechoicescanplayapartininfluencingtheriskofbreastcancerandevensmallchangesincorporateintoournormalday-to-dayactivitycanmakeadifference.”Sheadded:”Weknowthatthebestweapontoovercomingbreastcanceristheabilitytostopitoccurringinthefirstplace.Thechallengenowishowweturnthesefindingsintoactionandidentifyothersustainablelifestylechangesthatwillhelpuspreventbreastcancer.”Whichofthefollowingstatementsistrueaccordingtothepassage? A: Mostwomentakewalkingastheironlyrecreationalactivity. B: Walkingwastheonlyrecreationalactivityforabouthalfofthewomen. C: Thestudyaimstotrackthehealthconditionsofitssubjects. D: Irregularwalkingincreasedtheriskofbreastcancerinpost-menopausalwomen