Your company has 10 offices. The offices connect to the Internet by using a WAN link. The offices connect to each other by using a VPN connection. An Active Directory site exists for each office. You plan to deploy Exchange Server 2010. Each site will contain two Exchange Server 2010 servers. You need to recommend the placement of domain controllers and global catalog servers to meet thefollowing requirements： .Minimize the number of domain controllers .Must be able to deliver e-mail messages between users of the same office， if a domain controller and a WAN link fail simultaneously What should you recommend？（）

A. In each site， install two global catalog servers.
B. In each site， install two domain controllers. Enable Universal Group Membership caching for each site.
C. In each site， install two domain controllers. Create a publishing point for an offline address list on one Exchange server in each site.
D. In each site， install one domain controller that is configured as a global catalog server.Enable Universal Group Membership caching for each site.