Your network contains an Active Directory domain. The domain contains five domain
controllers. A domain controller named DC1 has the DHCP role and the file server role
installed.
You need to move the Active Directory database on DC1 to an alternate location.The
solution must minimize impact on the network during the database move.
What should you do first?

A.
Restart DC1 in Safe Mode.

B.
Restart DC1 in Directory Services Restore Mode.

C.
Start DC1 from Windows PE.

D.
Stop the Active Directory Domain Services service on DC1.

Explanation:
http://technet.microsoft.com/en-us/library/cc794895%28v=ws.10%29.aspx
Relocating the Active Directory Database Files
Applies To: Windows Server 2008, Windows Server 2008 R2
Relocating Active Directory database files usually involves moving files to a temporary
location while hardware updates are being performed and then moving the files to a
permanent location. On domain controllers that are running versions of Windows 2000
Server and Windows Server 2003, moving database files requires restarting the domain
controller in Directory Services Restore Mode (DSRM). Windows Server 2008 introduces
restartable Active Directory Domain Services (AD DS), which you can use to perform
database management tasks without restarting the domain controller in DSRM. Before you
move database files, you must stop AD DS as a service.