题目内容：
根据短文，回答题Thefutureofspaceexplorationdependsonmanythings．ItdependsonhowtechnologyevolveshowDoliticalforcesshapecompetitionandpartnershipsbetweennations，andhowimportantthepublicfeelsspaceexdlorationis．ThenearfuturewillseethecontinuationofhumanspaceflightinEarth’sorbitandunpilotedspacemghtwithintheso1arsystern．Pilotedspaceflighttootherplanets，orevenbacktothemoon,stillseemsfaraway．Anyflighttoothersolarsystemsisevenmoredistant'butahugeadVancemspacetechnologycoulddrivespaceexplorationintorealmscurrentlyexploredonlybysciencefiction．
The1968film2001：ASpacPOdysseydepictedcommercialshuttlesflyingtoandfromagiantwheel-shopedspacestationinorbharoundEarth，basesonthemoon，andapilotedmissiontoJupiter.Therealspaceactivitiesof2001willnotmatchthiscinematicvision，butthe21stcenturywillseeacontinuationofeffortstotransformhumanityintoaspacefaringspecies．
Perhapsthemostdifficultproblemspaceplannersfaceishowtofinanceavigorousprogramofpilotedspaceexploration.inEarth’sorbitandbeyond．Inl998nosinglegovernmentorinternationalenterprisehadplanstosendpeoplebacktothemoon，muchlesstoMars．SuchmissionsareunlikelytohappenuntiltheperceivedvalueexceedstheircosL
OnebeliefsharedbyanumberofspaceexplorationexpertsisthatfuturelunarandMartianexpeditionssheluldbeaimedatcreatingpermanentsettlements．Theresidentsofsuchoutpostswouldhaveto“liveofftheland”．0btainingsuchnecessitiesasoxygenandwaterfromtheharshenvironment．Onthemoon，pioneerscouldobtainoxygenbyheatinglunarsoil．Inl998theLunarProspectordiscoveredevidenceofsignificantdepositsofice，avaluableresourceforsettlers，mixedwithsollatthelunarpoles．OnMars，oxygencouldbeextracteelfromtheatmosphereandwatercouldcomefromburieddepositsofice．
Thefutureofpilotedlunarandplanetaryexplorationremainslargelyunknown．MostspaceexplorationscientistsbelievethatpeoplewillbeonthemoonandMarsbythemiddleofthe21stcentury，buthowtheygetthere，andthenatureoftheirvisits，isasubjectofcontinuingdebate．Clearly，keyadvanceswillneedtobemadeinloweringthecostofgettingpeopleoffEarth，thefirststepinanyhumanvoyagetootherworlds．
Aflighttoothersolarsystemswillbemadenlorepossibleby__________． A．technologicalbreak throughs
B．internationalcooperation
C．marketcompetition
D．publicpressure
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