Your company has a main office and four branch offices. You have an Active Directory Domain Services (AD DS) domain. All servers run Windows Server 2008 R2.All client computers run Windows 7. You virtualize applications by using Microsoft Application Virtualization (App-V). You need to ensure that all users access virtualized applications from their local branch office, and allow for active upgrades. Which should you install in each branch office?（）

A. a server with the File Services role installed
B. a server with the Web Server (IIS) role installed
C. Microsoft System Center Configuration Manager 2007 R2
D. Microsoft System Center Application Virtualization Streaming Server