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

A.
Modify the properties of the SOA record in the contoso.com zone.

B.
Create a NS record in the contoso.com zone.

C.
Create a delegation in the contoso.com zone.

D.
Create a standard secondary zone on a Global Catalog server.

Explanation:
http://technet.microsoft.com/en-us/library/cc771640.aspx
Understanding Zone Delegation
Domain Name System (DNS) provides the option of dividing up the namespace into one or
more zones, which can then be stored, distributed, and replicated to other DNS servers.
When you are deciding whether to divide your DNS namespace to make additional zones,
consider the following reasons to use additional zones:
You want to delegate management of part of your DNS namespace to another location or
department in your organization.
You want to divide one large zone into smaller zones to distribute traffic loads among
multiple servers, improve DNS name resolution performance, or create a more-fault-tolerant
DNS environment.
You want to extend the namespace by adding numerous subdomains at once, for example,
to accommodate the opening of a new branch or site.
..
When you delegate zones within your namespace, remember that for each new zone that
you create, you need delegation records in other zones that point to the authoritative DNS
servers for the new zone. This is necessary both to transfer authority and to provide correct
referral to other DNS servers and clients of the new servers that are being made
authoritative for the new zone.
..
Example: Delegating a subdomain to a new zone
As shown in the following illustration, when a new zone for a subdomain
(example.microsoft.com) is created, delegation from the parent zone (microsoft.com) is
needed.