You need to disable the global catalog on DC1

Your network contains an Active Directory forest. The forest contains two domains named
contoso.com and corp.contoso.com. All domain controllers run Windows Server 2012 R2 and are
configured as global catalog servers.
The corp.contoso.com domain contains a domain controller named DC1.
You need to disable the global catalog on DC1.
What should you do?

A.
From Active Directory Users and Computers, modify the properties of the DC1 computer account.

B.
From Active Directory Administrative Center, modify the properties of the DC1 computer account.

C.
From Active Directory Domains and Trusts, modify the properties of the corp.contoso.com
domain.

D.
From Active Directory Sites and Services, modify the NTDS Settings of the DC1 server object.

Explanation:
When you navigate your way to the Active Directory Sites and Services\Sites\SiteName\Servers then
in the details pane, right-click NTDS Settings of the selected server object, and then click Properties.
There will you get access to the Global Catalog check box to add the global catalog, or clear the
check box to remove the global catalog.
References:
http://technet.microsoft.com/en-us/library/cc755257.aspx