Your network containsan Active Directory forestnamed contoso.com.
The forest contains two domainsnamed contoso.comand child.contoso.com.
The forest contains two sitesnamed Seattleand Denver.
Both sitescontain users, client computers, and domain controllers from both domains.
The Seattle sitecontains the first domain controllerdeployed to the forest.
The Seattle site also contains the primary domain controller (PDC) emulatorfor both domains.
All of the domain controllersare configured as DNS servers.
All DNS zonesare replicated to all of the domain controllers in the forest.
The users in the Denver site reportthat is takes a long time to log onto their client computer when they
use their user principal name(UPN).
The users in the Seattlesite do not experience the same issue.
You needto reduce the amount of time it takes for the Denver users to log on to their client computer
by using their UPN.
What should you do?

A.
Reduce the cost of the site link between the Denver site and the Seattle site.

B.
Enable the global catalog on a domain controller in the Denver site.

C.
Enable universal group membership caching in the Denver site.

D.
Move a PDC emulator to the Denver site.

E.
Reduce the replication interval of the site link between the Denver site and the Seattle site.

F.
Add an additional domain controller to the Denversite.

Explanation:
Reference:
http://technet.microsoft.com/en-us/library/cc728188.aspx
Common Global Catalog Scenarios
The following events require a global catalog server:
(…)
User logon. In a forest that has more than one domain, two conditions require the global catalog during
user authentication:
1. When a user principal name (UPN) is used at logonand the forest has more than one domain, a global
catalog server is required to resolve the name.
2. (…)