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，theplatformlayerisafoundationforimplementingthe()layerforSaaSapplications．
A.connected B.imlemented C.optimized D.Virtualized正确答案A
