Cloudcomputingisaphraseusedtodescribeavarietyofcomputingconceptsthatinvolvealargenumberofcomputers()throughareal-timecommunicationnetworksuchastheInternet．Inscience，cloudcomputingisa()fordistributedcomputingoveranetwork，andmeansthe()torunaprogramorapplicationonmanyconnectedcomputersatthesametime．Thearchitectureofacloudisdevelopedatthreelayers：infrastructure，platform，andapplication，Theinfrastructurelayerisbuiltwithvirtualizedcompute，storage，andnetworkresources．Theplatformlayerisforgeneral-purposeandrepeatedusageofthecollectionofsoftwareresources．TheapplicationlayerisformedwithacollectionofallneededsoftwaremodulesforSaaSapplications．Theinfrastructurelayerservesasthe()forbuildingtheplatformlayerofthecloud．Inturn，theplatformlayerisafoundationforimplementingthe(请作答此空)layerforSaaSapplications．
A.resoruce
B.service
C.application
D.software
正确答案是C