Your network consists of an Active Directory forest that contains two domains. All servers
run Windows Server 2008 R2. All domain controllers are configured as DNS Servers.
You have a standard primary zone for dev.contoso.com that is stored on a member server.
You need to ensure that all domain controllers can resolve names from the dev.contoso.com
zone.
What should you do?

A.
On the member server, create a stub zone.

B.
On the member server, create a NS record for each domain controller.

C.
On one domain controller, create a conditional forwarder. Configure the conditional
forwarder to replicate to all DNS servers in the forest.

D.
On one domain controller, create a conditional forwarder. Configure the conditional
forwarder to replicate to all DNS servers in the domain.

Explanation:
http://technet.microsoft.com/en-us/library/cc730756.aspx

Understanding Forwarders
A forwarder is a Domain Name System (DNS) server on a network that forwards DNS
queries for external DNS names to DNS servers outside that network. You can also forward
queries according to specific domain names using conditional forwarders.
You designate a DNS server on a network as a forwarder by configuring the other DNS
servers in the network to forward the queries that they cannot resolve locally to that DNS
server. By using a forwarder, you can manage name resolution for names outside your
network, such as names on the Internet, and improve the efficiency of name resolution for
the computers in your network.
The following figure illustrates how external name queries are directed with forwarders.

Conditional forwarders
A conditional forwarder is a DNS server on a network that forwards DNS queries according
to the DNS domain name in the query. For example, you can configure a DNS server to
forward all the queries that it receives for names ending with corp.contoso.com to the IP
address of a specific DNS server or to the IP addresses of multiple DNS servers.
Further information:
http://technet.microsoft.com/en-us/library/cc794735%28v=ws.10%29.aspx
Assign a Conditional Forwarder for a Domain Name
http://technet.microsoft.com/en-us/library/cc754941.aspx
Configure a DNS Server to Use Forwarders