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