Your network contains an Active Directory domain. The domain contains a member server
named Server1 that runs Windows Server 2008 R2.
You need to configure Server1 as a global catalog server.
What should you do?

A.
Modify the Active Directory schema.

B.
From Ntdsutil, use the Roles option.

C.
Run the Active Directory Domain Services Installation Wizard on Server1.

D.
Move the Server1 computer object to the Domain Controllers organizational unit (OU).

Explanation:
Now it’s just a member server, so you’ll have to run dcpromo to start the Active Directory
Domain Services Installation Wizard in order to promote the server to a domain controller.
Only a domain controller can be a global catalog server.

http://technet.microsoft.com/en-us/library/cc728188.aspx
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.