Your company has an Active Directory forest. The network contains Exchange Server 2007 Service Pack 1 （SP1） and Exchange Server 2003 ServicePack 2 （SP2） servers. All domain controllers run Windows Server 2003 （x86） Service Pack 1 （SP1）. You plan to deploy Exchange Server 2010 on the network. You need to recommend changes to the servers so that you can deploy Exchange Server 2010 servers. What should you upgrade first？（）

• A、all domain controllers to Windows Server 2003 （x64） SP2
• B、all domain controllers to Windows Server 2008 （x86）
• C、all Exchange Server 2003 servers to Exchange Server 2007 SP2
• D、all Exchange Server 2007 SP1 servers to Exchange Server 2007 SP2