Theearthisabout4.6billionyearsold.Wehumans1 (live)ontheearthforalongtimeandwehavechangedourplanetalotinmanyways.Somethingswe'vedoneareverygoodfortheearth2 somearebad.
FewertreesAllovertheworldpeoplehavecutdown3 (million)oftrees.Whenitrainsorwhenthewindblowstheearth4 (take)away.Forestshavebecomedeserts.Somoreandmoresortsofanimalsandplantsaredisappearing.
TrafficandfactorypollutionInbigcitiescarsandbuseshavepollutedtheair.Nowmanypeopleincitieshavehealthproblems.Factorieshavealsopollutedthelandandthewater.Asa5 manyriversandlakesarenowdead.
Theozonelayer(臭氧层)Aroundtheearththere'saspecialkindofoxygen(O2)6 (call)"ozone"(O3).It'simportanttotheearth.Butnowairpollutionisdestroyingitandthathasmadeaverybigholeintheozonelayer.Toomuchharmfulradiation(辐射)fromthesunpasses7 theholeandreachestheearthdirectly.Thisisverydangerousbecausethiskindofradiation8 causecancer.
Morecarbondioxide(C02)Carbondioxideintheairhasincreasedalot.It9 (main)comesfromburningoilcoalandwood.Thishasformeda"blanket"aroundtheearth.Theheatfromthesuncan'tescapesothetemperatureisrising.Thatiscalled"thegreenhouseeffect(温室效应)".10 causestheleveloftheoceanstoriseandtheclimate(气候)oftheearthtochange.
Alltheseproblemsareveryserioussowemustdosomethingnow.
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