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