题目内容：
根据以下材料，回答题USresearchershavefoundtracesofanancientlakeonMarsrecently,increasinghopesofdis-coveringevidencethatbillionsofyearsagotheRedplanethostedlife.
Thelake,whichdatesbacksome3.4billionyears,appearstohavecoveredasmuchas80squaremilesandwasupto1,500feetdeep,saidtheteamfromtheUniversityofColorado.
"ThisisthefirstclearevidenceofshorelinesonthesurfaceofMars,"saidBoulder'sresearchassociate,GaetanoDiAchille,inastudypublishedinthelatesteditionofGeophysicalResearchLetters.
"Theidentificationoftheshorelinesandaccompanyinggeologicalevidenceallowsustocalculatethesizeandvolumeofthelake,whichappearstohaveformedabout3.4billionyearsago."
Analysisoftheimageshasshownthewatercarvedoutthecanyon(溪谷)inwhichitwasfound,whichthenopenedoutintoavalleydepositing(使淤积)sediment(沉积)whichformedadelta(三角洲).
"Findingshorelinesisagreatdiscoverytous,"saidassistantprofessorBrianHynek,addingitshowedthelakeexistedatatimewhenMarswasthoughttohavebeencoldanddry.
ScientistsbelievetheoldestsurfacesonMarsformedduringthewetandwarmeraknownastheNoaehanepoch,about4.1billionto3.7billionyearsago.
ThenewlydiscoveredlakeisbelievedtodatefromtheHesperianeraandpostdatestheendofthewarmandwetperiodonMarsby300millionyears,accordingtothestudy.
ScientistsbelievedeltasnexttothelakemaywellholdsecretsaboutpastlifeonMarsassuchplacesonEarthhavebecomethenaturaldepositsoforganiccarbonandothermarkersoflife.
ThesizeofthelakefoundonMarsis__________. A．80squaremiles
B．1,500squaremiles
C．3.4billionsquaremiles
D．300millionsquaremiles
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