Your network contains an Active Directory domain. The functional level of the domain is Windows Server 2003. The domain contains five domain controllers that run Windows Server 2008 and five  domain controllers that run Windows Server 2008 R2.   You need to ensure that SYSVOL is replicated by using Distributed File System Replication  （DFSR）.  What should you do first（）

• A、Run dfsrdiag.exe Pollad.
• B、Run dfsrmig.exe /SetGlobalState 0.
• C、Upgrade all domain controllers to Windows Server 2008 R2.
• D、Raise the functional level of the domain to Windows Server 2008.