Cloud computing is a phrase used to describe a variety of computing concepts that involve a large nu

Cloud computing is a phrase used to describe a variety of computing concepts that involve a large number of computers（ ） through a real-time communication network such as the Internet. In science, cloud computing is a （ ）for distributed computing over a network, and means the （ ） to run a program or application on many connected computers at the same time.The architecture of a cloud is developed at three layers: infrastructure, platform, and application. The infrastucture layer is built with virtualized computestorageand network resources. The platform lay-er is for general-purpose and repeated usage of the collection of software resources. The application layer is formed with a collection of all needed software modules for SaaS applications. The infrastucture layer serves as the（请作答此空） for building the platform layer of the cloud. In turn, the platform layer is founda-tion for implementing the （ ） layer for SaaS application.
A：network
B：foundation
C：software
D：hardware


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