单项选择题

A.Set the functional level of the forest to Windows Server 2003.
B.Prepare the legacy Exchange permissions from the Exchange Server 2010 installation source files.
C.Add the Exchange Server 2010 schema extensions by using the Exchange Server 2010 installationsource files.
D.Upgrade all domain controllers to Windows Server 2008, and then set the functional level of thedomain to Windows Server 2008.