Your company has a main office and five branch offices that are connected by WAN links. The  company has an Active Directory domain named contoso.com. Each branch office has a member  server configured as a DNS server. All branch office DNS servers host a secondary zone for  contoso.com.    
You need to configure the contoso.com zone to resolve client queries for at least four days in the  event that a WAN link fails.  
What should you do（）

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（）