Usability reviews evaluate a system or interface against established usability principles or standards to identify potential issues before user testing. A recognized criterion for such reviews includes adherence to usability standards such as ISO 9241 or the Web Content Accessibility Guidelines (WCAG). These standards are derived from years of research and user-centered design principles. Options A and C do not directly relate to usability. Functional requirements (option B) refer to what the system should do, not how usable it is. Hence, option D is correct as usability standards provide a consistent, objective basis for evaluating usability.