You have an Exchange Server organization. The organization contains servers that have Exchange Server
2010 and Exchange Server 2016 installed.You establish a hybrid deployment between Exchange Server and Microsoft Office 365.
Some users have on-premises mailboxes and personal archives in Exchange Online.
You discover that you are unable to use In-Place eDiscovery to search user mailboxes and Exchange Online
Archiving archives concurrently.
You need to recommend a solution to ensure that In-Place eDiscovery can search the mailboxes and the
personal archives concurrently.
What should you include in the recommendation?

A.
OAuth authentication

B.
an organization relationship

C.
a retention policy

D.
the Mailbox Replication service (MRS)

Explanation:
https://technet.microsoft.com/en-us/library/dd298021(v=exchg.160).aspx