Mandatory Access Control (MAC) is a model that uses a predefined set of access privileges for an object of the system. Access to an object is restricted on the basis of the sensitivity of the object and granted through authorization. Sensitivity of an object is defined by the label assigned to it. For example, if a user receives a copy of an object that is marked as "secret", he cannot grant permission to other users to see this object unless they have the appropriate permission. Answer: B is incorrect. DAC is an access control model. In this model, the data owner has the right to decide who can access the data. Answer: A is incorrect. Role-based access control (RBAC) is an access control model. In this model, a user can access resources according to his role in the organization. For example, a backup administrator is responsible for taking backups of important data. Therefore, he is only authorized to access this data for backing it up. However, sometimes users with different roles need to access the same resources. This situation can also be handled using the RBAC model. Answer: C is incorrect. There is no such access control model as Policy Access Control.