You need to decrease the amount of time it takes for the branch office users to logon

Your company has an Active Directory forest that contains two domains, The forest has
universal groups that contain members from each domain. A branch office has a domain
controller named DC1, Users at the branch office report that the logon process takes too
long.
You need to decrease the amount of time it takes for the branch office users to logon.
What should you do?

A.
Configure DC1 as a Global Catalog server.

B.
Configure DC1 as a bridgehead server for the branch office site.

C.
Decrease the replication interval on the site link that connects the branch office to the
corporate network.

D.
Increase the replication interval on the site link that connects the branch office to the
corporate network.

Explanation:
http://technet.microsoft.com/en-us/library/cc728188.aspx
What Is the Global Catalog?
The global catalog is a distributed data repository that contains a searchable, partial
representation of every object in every domain in a multidomain Active Directory Domain
Services (AD DS) forest. The global catalog is stored on domain controllers that have been
designated as global catalog servers and is distributed through multimaster replication.
Searches that are directed to the global catalog are faster because they do not involve
referrals to different domain controllers.
In addition to configuration and schema directory partition replicas, every domain controller
in a forest stores a full, writable replica of a single domain directory partition. Therefore, a

domain controller can locate only the objects in its domain. Locating an object in a different
domain would require the user or application to provide the domain of the requested object.
The global catalog provides the ability to locate objects from any domain without having to
know the domain name. A global catalog server is a domain controller that, in addition to its
full, writable domain directory partition replica, also stores a partial, read-only replica of all
other domain directory partitions in the forest. The additional domain directory partitions are
partial because only a limited set of attributes is included for each object. By including only
the attributes that are most used for searching, every object in every domain in even the
largest forest can be represented in the database of a single global catalog server.