You work as the enterprise exchange administrator at TestKing.com. TestKing.com makes use of Microsoft Exchange Server messaging solution. The TestKing.com network consists of a single ActiveDirectory forest. TestKing.com has a headquarters and two offices. Each of these offices contains an Active Directory. Theheadquarters contain six domain controllers that are configured to run Windows Server 2008 （x64）. Theother two offices contain one Windows Server 2008 read only domain controller （RODC）. The domain controllers in the forest are all configured as global catalog servers. You are planning toinstall an Exchange Server 2010 server at every office. You have received instructions to change theActive Directory to make sure that the Exchange servers’ branch office site is able to make a connectionto their respective domain controllers. What should you do？（）

• A、The best option is to use a writable domain controller in the two offices.
• B、The best option is to disable site link bridging for the forest and configure Exchange specific casts.
• C、The best option is to upgrade all RODCs to Windows Server 2008 （x64） RODCs.
• D、The best option is to use a DNS zone for each office.