Cloudcomputingisaphraseusedtodescribeavarietyofcomputingconceptsthatinvolvealargenumberofcomputers_()__throughareal-timecommunicationnetworksuchastheInternet.Inscience,cloudcomputingisa_()__fordistributedcomputingoveranetwork,andmeansthe_()_torunaprogramorapplicationonmanyconnectedcomputersatthesametime.Thearchitectureofacloudisdevelopedatthreelayers:infrastructure,platform,andapplication.Theinfrastructurelayerisbuiltwithvirtualizedcompute，storage，andnetworkresources.Theplatformlayerisforgeneral-purposeandrepeatedusageofthecollectionofsoftwareresources.TheapplicationlayerisformedwithacollectionofallneededsoftwaremodulesforSaaSapplications.Theinfrastructurelayerservesasthe_()__forbuildingtheplatformlayerofthecloud.Inturn,theplatformlayerisfoundationforimplementingthe_(请作答此空)__layerforSaaSapplication.
A.resource B.service C.application D.software正确答案C
