You plan to install Exchange Server 2010 Service Pack 1 (SP1) servers in an existing
Exchange Server 2007 organization. All servers will coexist in a single Active Directory site.
You need to identify which role must be transitioned to Exchange Server 2010 first.
Which role should you identify?

A.
Unified Messaging (UM)

B.
Hub Transport

C.
Client Access

D.
Mailbox