A corporate network includes a single Active Directory Domain Services (AD DS) domain.
The AD DS infrastructure is shown in the following graphic.

When the Montreal site domain controller is offline, authentication requests for Montreal
branch office users are sent to the Toronto site domain controller.

You need to ensure that when the Montreal Site domain controller is offline, authentication
requests forMontreal branch office users are sent to the Quebec City site domain controller.
What should you do?

A.
Create a site link bndge between the Montreal site and the Quebec City site.

B.
Enable the global catalog role on the Montreal site domain controller.

C.
Modify the Default Domain Policy Group Policy Object.

D.
Delete the Toronto-Montreal Site Link

Explanation:

http://technet.microsoft.com/en-us/library/cc772592.aspx
Enable Clients to Locate a Domain Controller in the Next Closest Site
You can modify the Default Domain Policy to enable Windows Vista and Windows Server
2008 clients in the domain to locate domain controllers in the next closest site if no domain
controller in their own site or the closest site is available.
To enable clients to locate a domain controller in the next closest site
1. Click Start, click Administrative Tools, and then click Group Policy Management.
2. If the User Account Control dialog box appears, confirm that the action it displays is what
you want, and then click Continue.
3. Double-click Forest:forest_name, double-click Domains, and then double-click
domain_name.
4. Right-click Default Domain Policy, and then click Edit.
5. In Group Policy Management Editor, in the console tree, go to Computer
Configuration/Policies/ Administrative Templates/System/Netlogon/DC Locator DNS
Records.
6. In the details pane, double-click Try Next Closest Site, click Enabled, and then click OK.

http://technet.microsoft.com/en-us/library/cc733142.aspx
Enabling Clients to Locate the Next Closest Domain Controller
If you have a domain controller that runs Windows Server 2008 or Windows Server 2008 R2,
you can make it possible for client computers that run Windows Vista, Windows 7, Windows
Server 2008, or Windows Server 2008 R2 to locate domain controllers more efficiently by
enabling the Try Next Closest Site Group Policy setting. This setting improves the Domain
Controller Locator (DC Locator) by helping to streamline network traffic, especially in large
enterprises that have many branch offices and sites.
By default, the Try Next Closest Site setting is not enabled. When the setting is not enabled,
DC Locator uses the following algorithm to locate a domain controller:
Try to find a domain controller in the same site.
If no domain controller is available in the same site, try to find any domain controller in the
domain.
If you enable the Try Next Closest Site setting, DC Locator uses the following algorithm to
locate a domain controller:
Try to find a domain controller in the same site.
If no domain controller is available in the same site, try to find a domain controller in the next
closest site. A site is closer if it has a lower site-link cost than another site with a higher sitelink cost.

If no domain controller is available in the next closest site, try to find any domain controller in
the domain.