Your company has a single Active Directory domain named intranet.contoso.com. All domain  controllers run Windows Server 2008 R2. The domain functional level is Windows 2000 native  and the forest functional level is Windows 2000.     You need to ensure the UPN suffix for contoso.com is available for user accounts.     What should you do first（）

• A、Raise the intranet.contoso.com forest functional level to Windows Server 2003 or higher.
• B、Raise the intranet.contoso.com domain functional level to Windows Server 2003 or higher.
• 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