Your company has a main office and a branch office. The company has a single-domain Active  Directory forest.  
The main office has two domain controllers named DC1 and DC2 that run Windows Server 2008  R2. The branch office has a Windows Server 2008 R2 read-only domain controller （RODC）named DC3. All domain controllers hold the DNS Server server role and are configured as Active  Directory- integrated zones. The DNS zones only allow secure updates.    
You need to enable dynamic DNS updates on DC3.    
What should you do（）

Your company has two domain controllers that are configured as internal DNS servers. All zones  on the DNS servers are Active Directory-integrated zones. The zones allow all dynamic updates.  You discover that the contoso.com zone has multiple entries for the host names of computers  that do not exist.    
You need to configure the contoso.com zone to automatically remove expired records.    
What should you do（）