Answer:
The correct answer to the question: How does ethos contribute to a persuasive argument, would be, D: It helps establish the writer´s credibility and good character.
Explanation:
Ethos is a Greek word that implies the understanding of the character of someone, or something. It speaks about the principles, the beliefs, and the characteristics, that form a circumstance, a person, a group, or an event. In literature, especially in persuasive argumentation, where you need to convince an audience about the validity of your point, nothing can be more important that building the "character" by clarifying where the ideas come from and what generates them. This is why the answer is the last one.