When should you consider performing a server NOS update?

A.
When the current use of the NOS requires a security update to be performed.

B.
When the update addresses current stability problems that are directly related to the operating system.

C.
When the security update involves areas of the OS that are actively being used by network operations.

D.
All of the above.

Explanation:
All of the above options detail circumstances under which you should seriously consider performing a server NOS update.
References:
Charles J. Brooks, Server+ Certification Exam Cram 2 (Exam SK0-002), QUE Publishing, Indianapolis, 2006, pp. 430-431.