Your company has a Windows Server 2003 Active Directory forest that contains a single domain. The functional level of the forest is set to Windows 2000 native. You have an Exchange organization that contains Exchange Server 2003 Service Pack 2 （SP2） andExchange Server 2007 Service Pack 2 （SP2） servers. You plan to transition the organization to Exchange Server 2010. You need to prepare Active Directory for the installation of the first Exchange Server 2010 server. What should you do？（）
- ASet the functional level of the forest to Windows Server 2003.
- BPrepare the legacy Exchange permissions from the Exchange Server 2010 installation source files.
- CAdd the Exchange Server 2010 schema extensions by using the Exchange Server 2010 installationsource files.
- DUpgrade all domain controllers to Windows Server 2008， and then set the functional level of thedomain to Windows Server 2008.