Final answer:
Princess Diana's credibility to speak on landmines is established by her firsthand experience witnessing the effects of landmines in Angola.
Step-by-step explanation:
Princess Diana's credibility (ethos) to speak on the topic of landmines is established by the fact that she witnessed the effects of landmines in Angola when she visited. This firsthand experience gives her personal knowledge and a deeper understanding of the issue. It also shows her empathy and concern for the victims of landmines.
Learn more about Princess Diana's credibility to speak on landmines