What should you identify?

You have an Exchange Server 2016 organization.
You plan to migrate some of the users to Exchange Online.
You run the Microsoft Office 365 Hybrid Configuration Wizard and you discover that the GetFederationInformation cmdlet fails to retrieve the required information.
You need to identify which DNS record must be configured to resolve the failure.
What should you identify?

A.
an MX record for SMTP domain

B.
an A record for a Mailbox server

C.
a PTR record for the Mailbox server

D.
an A record for Autodiscover

Explanation:
http://blogs.technet.com/b/mikehall/archive/2013/08/21/office-365-insight-into-the-hybrid-configuration-wizardpart-2.aspx