Your company, Contoso, Ltd., has a main office and a branch office. The offices are
connected by a WAN link.Contoso has an Active Directory forest that contains a single
domain named ad.contoso.com.
The ad.contoso.com domain contains one domain controller named DC1 that is located in
the main office. DC1 is configured as a DNS server for the ad.contoso.com DNS zone. This
zone is configured as a standard primary zone.
You install a new domain controller named DC2 in the branch office. You install DNS on
DC2.
You need to ensure that the DNS service can update records and resolve DNS queries in
the event that aWAN link fails.
What should you do?

A.
Create a new secondary zone named ad.contoso.com on DC2.

B.
Create a new stub zone named ad.contoso.com on DC2.

C.
Configure the DNS server on DC2 to forward requests to DC1.

D.
Convert the ad.contoso.com zone on DC1 to an Active Directory-integrated zone.

Explanation:
Three answers don’t make sense, leaving us with the one that works.
Create a new secondary zone named ad.contoso.com on DC2.
This would create a read-only zone, so it couldn’t be updated
Create a new stub zone named ad.contoso.com on DC2.
This stub zone would contain source information about authoritative name servers for its
zone only, being DC1, but that one would be unavailable in the WAN link fails.
Configure the DNS server on DC2 to forward requests to DC1.
This doesn’t help if the WAN link fails and DC1 is unavailable.