Answer:
A. OU
Explanation:
An organization unit (OU) is used to group objects that are related, having similar administrative and security requirements within a domain. It provides a way of classifying objects in a directory, such as differentiating between objects with the same name or managing and creating objects. An OU can be nested into another OU, thus it can be used to create a hierarchy within an organization.
Firewalls are connected with a network device which blocks untrusted network forming a barrier in between trusted and un-trusted network.
I would say none of the above as A, B, and C do not seem like sensible answers.
