As a security consultant, what are some of the things you would recommend to a company to ensure DNS security?

As a security consultant, what are some of the things you would recommend to a company to ensure DNS security? Select the best answers.

A.
Use the same machines for DNS and other applications

B.
Harden DNS servers

C.
Use split-horizon operation for DNS servers

D.
Restrict Zone transfers

E.
Have subnet diversity between DNS servers