The sentence that is an example of using a person as a presentation aid is B, that is, "demonstrating the latest haircut techniques using a friend as a model". This is the case because the audience will be actually seeing the result once you finish your job at the same you'll be explaining how you do it. Therefore, the will get a clear picture of how to apply the new techniques, just as presentations do. The fact is that images make presentations better, they have the power to trigger an immediate response; in addition, you will definitely get the attention of the public.