Your network contains an Active Directory domain named contoso.com. Contoso.com
contains two sites named Site1 and Site2. Site1 contains a domain controller named DC1.
In Site1, you install a new domain controller named DC2. You ship DC2 to Site2.
You discover that certain users in Site2 authenticate to DC1.
You need to ensure that the users in Site2 always attempt to authenticate to DC2 first.
What should you do?

A.
From Active Directory Users and Computers, modify the Location settings of the DC2
computer object.

B.
From Active Directory Sites and Services, modify the Location attribute for Site2.

C.
From Active Directory Sites and Services, move the DC2 server object.

D.
From Active Directory Users and Computers, move the DC2 computer object.

Explanation:
DC2 may be shipped to Site2, but it’s not yet associated properly with Site2 in Active
Directory.
Reference1)
http://technet.microsoft.com/en-us/library/cc816674.aspx
To move a server object to a new site
1. Open Active Directory Sites and Services.
2. In the console tree, expand Sites and the site in which the server object resides.
3. Expand Servers to display the domain controllers that are currently configured for that
site.
4. Right-click the server object that you want to move, and then click Move.
5. In Site Name, click the destination site, and then click OK.
6. Expand the site object to which you moved the server, and then expand the Servers
container.
7. Verify that an object for the server that you moved exists.
8. Expand the server object, and verify that an NTDS Settings object exists.
Reference2)
http://technet.microsoft.com/en-us/library/cc754697.aspx

Using sites
Sites help facilitate several activities, including:
(…)
Authentication. Site information helps make authentication faster and more efficient. When a
client logs on to a domain, it first requests a domain controller in its local site for
authentication. By establishing sites, you can ensure that clients use domain controllers that
are nearest to them for authentication, which reduces authentication latency and traffic on
wide area network (WAN) connections.