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.

Explanation:
http://support.microsoft.com/kb/243629
HOW TO: Add UPN Suffixes to a Forest
Adding a UPN Suffix to a Forest
Open Active Directory Domains and Trusts.
Right-click Active Directory Domains and Trusts in the Tree window pane, and then click
Properties.
On the UPN Suffixes tab, type the new UPN suffix that you would like to add to the forrest.
Click Add, and then click OK.
Now when you add users to the forest, you can select the new UPN suffix to complete the
user’s logon name.
APPLIES TO
Microsoft Windows 2000 Server
Microsoft Windows 2000 Advanced Server
Microsoft Windows 2000 Datacenter Server