Your network contains a DNS server that runs Windows Server 2008 R2. You open the Forwarders settings of the DNS server and discover that the option to add forwarders is disabled.
You need to add forwarders to the DNS server.
What should you do first?

A.
Enable BIND secondaries.

B.
Delete the "." (root) zone.

C.
Create a GlobalNames zone.

D.
Delete all conditional forwarders.