What should you modify?

You have an Exchange Server organization that contains Exchange Server 2010 servers and Exchange
Server 2013 servers. You have a Microsoft Lync Server 2010 environment that is integrated with
Unified Messaging (UM) services.
You have an Exchange Server 2010 server named EX1 that has the Unified Messaging server role
installed.
You are migrating the UM services to Exchange Server 2013.
You need to prevent EX1 from providing call answering services during the migration.
What should you modify?

A.
the UM mailbox policies

B.
the UM auto attendants

C.
the UM dial plans

D.
the UM hunt groups