Your network contains an Active Directory forest. All domain controllers run Windows Server 2008.  You have an Exchange organization that consists of the servers shown in the following table.You plan to implement moderated transport for distribution groups in the organization.  You need to recommend changes to the organization to support the planned implementation.  What should you recommend？（）

• A、Upgrade Server3 to Exchange Server 2010.
• B、Install Windows Server 2008 R2 global catalog servers.
• C、Replace all distribution groups with dynamic distribution groups.
• D、Use Server4 as the expansion server for all moderated distribution groups.