Domains provide which of the following functions?

A.
Creating logical boundaries

B.
Easing the administration of users, groups, computers, and other objects

C.
Providing a central database of network objects

D.
All of the above

Explanation:
http://technet.microsoft.com/en-us/library/cc756901%28v=ws.10%29.aspx
Active Directory Logical Structure Background Information
Before you design your Active Directory logical structure, it is important to understand the Active Directory
logical model. Active Directory is a distributed database that stores and manages information about network
resources, as well as application-specific data from directory enabled applications. Active Directory allows
administrators to organize elements of a network (such as users, computers, devices, and so on) into a
hierarchical containment structure. The top-level container is the forest. Within forests are domains,and within
domains are organizational units. This is called the logical model because it is independent of the physical
aspects of the deployment, such as the number of domain controllers required within each domain and network
topology.

Figure 2.2 Relationship Between Active Directory Forests, Domains, and OUs