Your network contains an Active Directory forest.
The forest contains three domains.
All domain controllershave the DNS Server server role installed.
The forest contains three sitesnamed Site1, Site2, and Site3.
Each sitecontains the users, client computers, and domain controllers of each domain.
Site1contains the first domain controller deployed to the forest.
The sites connectto each other by using unreliable WAN links.
The users in Site2 and Site3 reportthat it takes a long time to log onto their client computer when they
use theiruser principal name (UPN).
The users in Site1 do not experience the same issue.
You need to reduce the amount of time it takes for the Site2 users and the Site3 users to log on to their
client computer by using their UPN.
What should you do?

A.
Configure a global catalog server in Site2 and a global catalog server in Site3.

B.
Reduce the replication interval of the site links.

C.
Move a primary domain controller (PDC) emulator to Site2 and to Site3.

D.
Add additional domain controllers to Site2 and toSite3.

E.
Reduce the cost of the site links.

F.
Enable universal group membership caching in Site2 and in Site3.

Explanation:
Quite similar to K/Q9.
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. (…)