You need to recommend a solution to ensure that users can access their mailbox on EX1 or EX4 during the migration

You have an Exchange Server 2010 organization that contains three servers. The servers
are configured as shown in the following table.

Microsoft Outlook is configured to connect to an FQDN of mail.adatum.com.
Mail.adatum.com resolves to the IP address of a Layer 7 hardware load balancer. The
hardware load balancer is configured to send traffic to EX2 and EX3. You deploy an
Exchange Server 2013 Mailbox server and an Exchange Server 2013 Client Access server.
You plan to migrate all mailboxes to Exchange Server 2013. You need to recommend a
solution to ensure that users can access their mailbox on EX1 or EX4 during the migration.
What should you do?

A.
Create a Client Access server array that contains EX1 and EX5.

B.
Modify the autodiscover.contoso.com resource record to point to EX5.

C.
Modify the properties of the hardware load balancer to point to EX5.

D.
Create a DNS record named legacy.contoso.com in the internal DNS zone.