问题：

[单选] Your company has a single Active Directory domain named intranet.contoso.com. All domain controllers run Windows Server 2008. The domain functional level and the forest functional level are set to Windows 2000 native mode. You need to ensure the UPN suffix for contoso.com is available for user accounts. What should you do first（）

A . Raise the contoso.com forest functional level to Windows Server 2003 or Windows Server 2008.
B . Raise the contoso.com domain functional level to Windows Server 2003 or Windows Server 2008.
C . Add the new UPN suffix to the forest.
D . Change the Primary DNS Suffix option in the Default Domain Controllers Group Policy Object （GPO） to contoso.com.