Answer:
C. By quoting a public figure to establish credibility
Step-by-step explanation:
Ethos is exemplified as the literary technique employed to persuade the audience to believe in the claim or argument proposed by the author or speaker by appealing to their ethics or moral conduct. It is described as one of the three 'modes of persuasion' as proposed by Aristotle that is based on the speaker's character or credibility, the other two are logos (appeal to logic) and pathos (appeal to emotion).
As per the question, in the given passage the author Geoffrey Lean employs ethos 'by quoting a public figure to establish credibility' as he invokes authority that aids to establish the credibility of his claim and persuade the readers ethically. Thus, option C is the correct answer.