Peopleandthesourcesofairpollutionarefoundinthesameplaces.Thismeansthatcitieswithlargepopulationshavethebiggestproblemofdirtyair.Airpollutioniscausedbymanydifferentthings.Amajorsourceofairpollutionisthegasfumesfromcars.Statisticsshowthat93percentofallautotripsarewithincities.Anothermajorsourceofdirtyairistheburningofcoalandoilforenergy.Thisenergyisneededtomakeelectricity.Ofcoursemuchmoreelectricityisusedinthecitythaninthecountry.
Ontheaveragewethrowawaymoretrashandgarbagethantheyearbefore.Theburningofgarbagecontributestoairpollution.Manymajorindustriesarealsoresponsibleforthedirtyairinthearoundcities.Thefumesfromironsteelchemicalandpetroleumproductionaddparticlestotheair.
Theeffectsofairpollutionrangefrommildheadachestodeath.Thelevelsofpollutionfoundinheavyfortrafficmaycauseheadachesforlossofclearvision.Wherevercoalandoilareusedforfuelfumesmaykilltreesandplantsandcausemetaltocorrode.Insomeofthelargercitiesthesefumesendangertheliveofhumanbeingsbycontributingtolungdiseasesandcausingearlydeath.
67.Thekeypointofthepassageisthat_________.
A.thecauseofairpollutionispeople
B.thecausesandtheeffectsofairpollutionarebothfoundincities
C.theeffectsofairpollutionrangefromheadachestodeath
D.airpollutioniscausedbydirtyair
68.Whatisthepurposeofthispassage?
A.topersuadepeopletostoppollutingtheair
B.totellthecausesofairpollution
C.totellwhycitiesarebadplacestolive
D.todescribewhycitiesarebadplacestolive
69.Whyisairpollutionmoregraveinthecitythaninthecountry?
A.Becausetherelargerpopulationsincities.
B.Becausetheairinthecityisdirty.
C.Becausetherearemorecarsinthecity.
D.Becausetherearemuchmoregasfumesfromcarsandburningofcoalandoilforenergyinthecitythaninthecountry.
70.Thefumesfromcoalandoilmaycausemetal______.
A.toturnblack B.tobecomerusty C.tocorrode D.totwist
71.Inlargercitiesthe