You are the messaging engineer for your company. The company network contains an Active Directory forest that contains three domains. Each domain contains at least one Microsoft Exchange Server 2003 server. All mail-enabled groups are configured as global distribution groups. You plan to transition from Exchange Server 2003 to Exchange Server 2007. You need to recommend a solution that ensures that all mail-enabled groups can be expanded from any Exchange Server 2003 server or any Exchange Server 2007 server. What should you recommend?

A.
Convert all global distribution groups to global security groups.

B.
Convert all global distribution groups to universal distribution groups.

C.
Configure all global distribution groups to require that senders are authenticated.

D.
Configure all global distribution groups to send delivery reports to the message originator.

Explanation:
In Exchange 2007, you can create or mail-enable only universal distribution groups. You may have mail-enabled groups migrated from previous versions of Exchange that arent universal groups. These can still be managed using EMC or the EM Shell.

http://technet.microsoft.com/en-us/library/bb201680.aspx

http://technet.microsoft.com/en-us/library/bb125256.aspx