Final answer:
(c) Whistles. When Brom first sees the mark on Eragon's hand, he whistles as Eragon walks away. This response from Brom hints at his recognition of Eragon's destiny as a Dragon Rider in the story of 'Eragon.'
Step-by-step explanation:
The subject of the question is the book Eragon by Christopher Paolini, which falls under the category of English, specifically in literature. The context of the question is when Brom first sees the mark on Eragon's hand, which is significant in the story as it identifies Eragon as a Dragon Rider. After Brom notices the mark and Eragon walks away, the correct answer is (c) Whistles. Brom's action of whistling is indicative of his knowledge and recognition of the importance of the mark, though at this point in the story, he does not openly disclose his awareness to Eragon. This detail is part of the unfolding narrative where Eragon's true identity and destiny are gradually revealed, contributing to the development of the plot.