懂你英语Level3unit3

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1、实用文档Level3unit3part1ListeningTherearemanyformsoflifeonEarth,includinghumanbeings.Lifeexistsinavarietyofconditions.Someformsoflifeliveinawateryenvironment,liketheoceans.Otherformsoflifecanbefoundinverydryareas,likedeserts.However,foranyformoflifetoexist,conditionsmustberight.Whenconditionsarenotright

2、,thatformoflifewillbecomeextinct.Tobecomeextinctmeanstodieoutcompletely.-Whatmustberightforlifetoexist?-Conditions.-Whathappensifconditionsarenotright?–Lifecannotexist.Conditionsmustberightforlifetoexist.Millionsofyearsago,therewereformsoflifethatnolongerexist.Whenconditionschanged,theseformsoflifed

3、iedout.Oneextinctioneventhappenedabout250millionyearsago.Thiswasthelargestextinctioneventofalltime.Manyformsoflifebecameextinct.96%ofalllifeintheoceansdiedout.Mostinsectsalsobecameextinct.Thiseventhappenedoveraperiodofseveralmillionyears.-Whathappenedabout250millionyearsago?–Manyformsoflifebecameext

4、inct.-Whathappensinanextinctionevent?–Manyformsoflifebecameextinct.Thecausesofthisextinctioneventarestillunknown.Possiblecausesincludelargevolcaniceruptionsandglobalwarming.Somescientistsbelievethattherewereseveralcauses.文案大全实用文档Theybelievethataseriesofeventscausedtheextinctions.Scientistsareworking

5、tobetterunderstandwhatreallyhappened.-Whatistheonepossiblecauseofthisevent?–Volcaniceruptions.Inmoderntimes,wehumansfacechangingconditions.Forhumanstolive,weneedcleanairandcleanwater.Pollutionisnowagrowingproblemaroundtheworld.Pollutionpoisonstheairandwaterthatwedependon.Pollutedairmakespeoplesickan

6、dafraidtogooutside.Pollutedwaterpoisonsourfoodsupply.Asaresult,weneverknowwhichfoodsaresafetoeat.Humanbeingscannotliveinapoisonedenvironment.Therefore,pollutionisamajorthreattoourexistence.-Whatdohumansneedtolive?–Cleanairandcleanwater.-Whatpoisonstheairandwater?–Pollution.Humansneedtemperaturestobe

7、inacomfortablerange.Tobeinacomfortablerangemeanstobeneithertoohotnortoocold.Withglobalwarming,globaltemperaturesarerising.Astemperaturesrise,thepolaricecapswillmelt.Asthepolaricecapsmelt,oceanlevelswi