Your company has an Active Directory directory service domain. The domain functional level is Windows Server 2003. The company has a main office with two domain controllers （DCs）. Users log on to client computers by using user principal names （UPNs）. You plan to set up a new branch office with one domain controller.  You need to ensure that when the branch office domain controllers connection to the main office is unavailable， users in the branch office can log on to the domain.  What should you do？（）

• A、 Add a new domain controller in the branch office.
• B、 Configure the branch office domain controller as a global catalog server.
• C、 Transfer the RID Master role to the branch office domain controller.
• D、 Transfer the Infrastructure Master role to the branch office domain controller.