题目内容：
根据以下材料，回答题Thefutureofspaceexplorationdependsonmanythings.Itdependsonhowtechnologyevolves,howpoliticalforcesshapecompetitionandpartnershipsbetweennations,andhowimportantthe
publicfeelsspaceexplorationis.ThenearfuturewillseethecontinuationofhumanspaceflightinEarth'sorbitandunpilotedspaceflightwithintheSolarsystem.Pilotedspaceflightto
'otberplanets,orevenbacktothemoon,stillseemsfaraway.AnyflighttootherSolarsystemsisevenmoredistant,butahugeadvanceinspacetechnologycoulddrivespaceexploration
intorealmscurrentlyexploredonlybysciencefiction.
The1968film2001:ASpaceOdysseydepictedcommercialshuttlesflyingtoandfromagiantwheel-shapedspacestationinorbitaround,Earth,basesonthemoon,andapilotedmissiontoJupiter.Therealspaceactivitiesof2001willnotmatchthiscinematicvision,butthe21stcenturywillseea
continuationofeffortstotransformhumanityintoaspacefaringspecies.
Perhapsthemostdifficultproblemspaceplannersfaceishowtofinanceavigorousprogramofpilotedspaceexploration,inEarth'sorbitandbeyond.In1998nosinglegovernmentor
internationalenterprisehadplanstosendpeoplebacktothemoon,muchlesstoMars.Suchmissionsareunlikelytohappenuntiltheperceivedvalueexceedstheircost.
OnebeliefsharedbyanumberofspaceexplorationexpertsisthatfuturelunarandMartianexpeditionsshouldbeaimedatcreatingpermanentsettlements.Theresidentsofsuchoutpostswouldhave
to"liveofftheland,"obtainingsuchnecessitiesasoxygenandwaterfromtheharshenvironment.Onthemoon,pioneerscouldobtainoxygenbyheatinglunarSoil.In1998the
LunarProspectordiscoveredevidenceofsignificantdepositsofice,avaluablereSourceforsettlers,mixedwithSoilatthelunarpoles.OnMars,oxygencouldbeextractedfromtheatmosphere
andwatercouldcomefromburieddepositsofice.
Thefutureofpilotedlunarandplanetaryexplorationremainslargelyunknown.MostspaceexplorationscientistsbelievethatpeoplewillbeonthemoonandMarsbythemiddleofthe21stcentury,
buthowtheygetthere,andthenatureoftheirvisits,isasubjectofcontinuingdebate.Clearly,keyadvanceswillneedtobemadeinloweringthecostofgettingpeopleoffEarth,thefirststepinany
humanvoyagetootherworlds.
AflighttootherSolarsystemswillbemademorepossibleby A．technologicalbreakthroughs.
B．internationalco-operation.
C．marketcompetition.
D．publicpressure.
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