In "Resistance to Civil Government," Henry David Thoreau uses ethos in order to help his audience gain trust in him. Thoreau uses his own personal experience in order to demonstrate his knowledge of his topic and his own personal connection to it. By using ethos in this rhetorical situation, Thoreau is attempting to inspire trust in his readers and establish his own credibility.
Since this drawing is his way of reminding her that she and their garden are "as safe as a missel thrush", it makes her one of the many creatures whose secrets he keeps faithfully. So, having that in mind, I would say the correct answer is A) his trustworthiness.
