Your network contains an Active Directory domain named contoso.com. The network
contains a domain controller named DC1 that has the DNS Server server role installed. DC1
has a standard primary DNS zone for contoso.com.
You need to ensure that only client computers in the contoso.com domain will be able to add
their records to the contoso.com zone.
What should you do first?

A.
Sign the contoso.com zone.

B.
Modify the Security settings of DC1.

C.
Modify the Security settings of the contoso.com zone.

D.
Store the contoso.com zone in Active Directory.

Explanation:
Only Authenticated users can create records when zone is stored in AD
Secure dynamic updates allow an administrator to control what computers update what
names and prevent unauthorized computers from overwriting existing names in DNS.
References:

Training Guide: Installing and Configuring Windows Server 2012 R2: Chapter 6: Network
Administration, Lesson 2: Implementing DNSSEC, p. 237
http://technet.microsoft.com/en-us/library/cc731204(v=ws.10).aspx
http://technet.microsoft.com/en-us/library/cc755193.aspx