The unique feature of attribute-based access control (ABAC) that is represented by the option C is that a user is granted access to a system at a particular time of day. ABAC is a type of access control model that uses attributes as the basis for granting or denying access to resources or actions. Attributes are properties or characteristics of entities, such as users, devices, resources, or actions, that can be used to describe or identify them. Attributes can be static or dynamic, and can be derived from various sources, such as identity, environment, location, or time. ABAC can use any combination of attributes to define the access policies and rules, and to evaluate the access requests. ABAC is more flexible and granular than other access control models, such as Mandatory Access Control (MAC), Discretionary Access Control (DAC), or Role Based Access Control (RBAC), which use labels, owners, or roles as the basis for access control. A unique feature of ABAC is that it can use the time attribute to grant or deny access to a system, based on the particular time of day, such as the working hours, the holidays, or the weekends56. References: CISSP CBK, Fifth Edition, Chapter 5, page 443; CISSP Practice Exam - FREE 20 Questions and Answers, Question 18.