You have an Exchange Server 2013 organization that contains two servers named EX1 and EX2. EX1 and EX2 are members of a database availability group (DAG) named DAG1.
Your organization contains several managed availability overrides.
Both EX1 and EX2 have a copy of a mailbox database named MBX1. МBХ1 is active on EXl.
You discover that MBX1 on EX2 has a status of ServiceDown.
You need to restore the status of MBX1 on EX2 to healthy as quickly as possible.
What should you do?

A.
Start the Microsoft Exchange Information Store Service.

B.
Run Start-Service MSExchangeIS.

C.
Run Start-Service MSExchangeRepl.

D.
Start the Microsoft Exchange Mail Replication Service.

Explanation:
http://www.solarwinds.com/documentation/en/flarehelp/sam/content/
samagappinsightforexchangemailboxdatabasestatus.htm
https://technet.microsoft.com/en-us/library/ee423542(v=exchg.141).aspx