Your network contains a single Active Directory domain named contoso.com. The functional level of the domain is Windows 2000 mixed.  You have a domain controller named DC1 that runs Windows Server 2003 Service Pack 2 （SP2）. DC1 hosts a standard primary zone for contoso.com. You need to ensure that only computers in the contoso.com domain can register host records in the contoso.com zone.  What should you do？（）

• A、Convert contoso.com to a secondary zone.
• B、Convert contoso.com to an Active Directory-integrated zone. Set dynamic updates for the zone to Secure only.
• C、Convert contoso.com to an Active Directory-integrated zone. Set dynamic updates for the zone to Nonsecure and secure.
• D、Change the domain functional level to Windows Server 2003. Set dynamic updates for the zone to Nonsecure and secure.