which of the following functions?

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.