Your company has a main office and ten branch offices. Your network consists of a single domain Active Directory forest. An Active Directory site exists for each office. The main office contains five domain controllers that run Windows Server 2008 （x64）. Each branch office contains one read-only domain controller （RODC） that runs Windows Server 2008（x86）. All domain controllers are configured as global catalog servers. You plan to deploy one Exchange Server 2010 server in each site. You need to recommend changes to Active Directory to support the planned deployment. The solution must ensure that Exchange servers in each branch-office site connect to their local domain controllers. What should you recommend？（）

A. Implement a DNS zone for each office.
B. Change all RODCs to Windows Server 2008 （x64） RODCs.
C. Implement a writable domain controller in each branch office.
Disable site link bridging for the forest and configure Exchange-specific costs.