Your network contains an Active Directory domain named contoso.com.   You  plan  to  deploy  a  child  domain  named  sales.contoso.com.  The  domain  controllers  in sales.contoso.com will be DNS servers for sales.contoso.com.   You need to ensure that users in contoso.com can connect to servers in sales.contoso.com by using fully  qualified domain names （FQDNs）.   What should you do（）

• A、Create a DNS forwarder.
• B、Create a DNS delegation.
• C、Configure root hint servers.
• D、Configure an alternate DNS server on all client computers.