Cloud computing is a phrase used to describe a variety of computing concepts that involve a large number of computers (1) through a real-time communication network such as the Internet. In science, cloud computing is a (2)for distributed computing over a network, and means the (3) 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 infrastructure layer is built with virtualized compute, storage, and network resources. The platform layer 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 infrastructure layer serves as the (4)for building the platform layer of the cloud. In turn, the platform layer is a foundation for implementing the (5) layer for SaaS applications.
空白（2）处应选择（）
A.replacement
B.switch
C.substitute
D.synonym（同义词）
参考答案：A
解析：参考译文：本题考查对英语资料的阅读理解。本段英文简要介绍云计算相关概念。云计算是用来描述各种计算概念的短语，包括大量计算机通过网络相互连接以实现分布计算，意思是同时在很多互联的计算机上运行程序或应用的能力。云的架构分为基础设施层、平台层和应用层三层。基础设施层由虚拟计算、存储和网络资源构成。平台层用于一组软件资源重复使用的通用目的。应用层由一组所需的软件模块构成，即软件即服务（SaaS）。基础设施层作为构建平台层的基础。相反，平台层是应用层的基础，为SaaS应用实现应用层。