IfthepopulationoftheEarthkeepson__61._(increase)atitspresentrate,therewill__62._(event)notbeenoughresourceslefttosupportlifeontheplanet.Bythemiddleofthe21stcentury,ifpresenttrendscontinue,we__63_(use)upalltheoilthatdriveourcarsforexample.EvenifscientistsdevelopnewwaysoffeedingthehumanracethecrowdedconditionsonEarthwillmakeit__64 (necessity)forustolookforsomewhereelse.But__65._oftheotherplanetsinoursolarsystemarecapableofsupportinglifeatpresent.Onepossiblesolutiontotheproblem,__66._,hasrecentlybeensuggestedbyanAmericanscientistProfessorCarlSagan.Sagarnbelievesthat__67._theEarth’sresourcesarecompletely__68_(exhaust),itwillbepossibletochangetheatmosphereofVenusand__69_createanewworldalmostaslargeasEarthitself.Somethingisdifficult.VenusismuchhotterthantheEarth.__70._,thereisonlyatinyamountofwaterthere.
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