Which of the following PR planning models is NOT mentioned in the provided content?

The correct answer is GNU because it is not recognized as a standard public relations planning model among the other options provided. In public relations practice, models such as RPIE (Research, Planning, Implementation, Evaluation), RACE (Research, Action, Communication, Evaluation), and ROPE (Research, Objectives, Programming, Evaluation) are commonly utilized frameworks that guide practitioners in developing their strategic communication efforts. Each of these models emphasizes key components of effective PR planning and execution. GNU, on the other hand, is not widely known or referenced in the context of public relations frameworks, which is why it stands out as the choice not mentioned in the content.