A “usability test participant” …

A usability test participant is a person selected to represent the target user group and asked to perform specific tasks in a usability test. Their actions, reactions, and feedback help identify usability issues and evaluate the system’s effectiveness, efficiency, and user satisfaction. This role is strictly observational and does not involve organizing, observing, or setting up the test. Options A, B, and C describe other roles (e.g., technical support, observers, or moderators). Only option D accurately reflects the definition of a usability test participant.