You have an Exchange Server 2013 organization that contains the servers configured as shown in the following
table.

All mailbox servers are members of a database availability group (DAG) named DAG1. DAG1 has Datacenter
Activation Coordination (DAC) mode enabled. The data center in Dallas experiences a power failure, causing
quorum to be lost.
You need to mount the databases in the data center in Houston.
Which command should you run first?

A.
Stop-DatabaseAvailabilityGroup -Identity DAG1 -MailboxServer EX1 -ConfigurationOnly.

B.
Restore-DatabaseAvailabilityGroup -Identity DAG1 -ActiveDirectorySite Exchange-Site –
AlternateWitnessServer -AlternateWitnessDirectory D:\\DAG1

C.
Stop-DatabaseAvailabilityGroup -Identity DAG1 -ActiveDirectorySite Exchange-Site

D.
Stop-Service -DisplayName ClusSvc -Force.

Explanation:
First step: Terminating a Partially Failed Datacenter
When the DAG is in DAC mode, the specific actions to terminate any surviving DAG members in the primary
datacenter are as follows:
The DAG members in the primary datacenter must be marked as stopped in the primary datacenter. Stopped is
a state of Active Manager that prevents databases from mounting, and Active Manager on each server in the
failed datacenter is put into this state by using the Stop- DatabaseAvailabilityGroup cmdlet.
Datacenter Switchovers
https://technet.microsoft.com/en-us/library/dd351049(v=exchg.150).aspx