Final answer:
The name of Darrow's horse is not explicitly provided in the given references, but it is inferred to be Black Star. None of the options a) Shadow, b) Storm, c) Obsidian, and d) Eo match the references provided, implying that Black Star is the best name based on available information.
Step-by-step explanation:
The name of Darrow's horse is Black Star. The text excerpts provided suggest that Jane Withersteen, the character who owns Black Star, values him greatly for his qualities, and the name likely emphasizes his notable features and the connection she feels with him.
Black Star is described in a way that emphasizes speed, as seen by phrases like "Swiftest horse on the sage!" and scenarios where Jane allows Black Star to have free running on the open trail. Unfortunately, the name choices provided in the question a) Shadow, b) Storm, c) Obsidian, and d) Eo do not match the information given in the texts, so none of these options accurately answer the question based on the references provided.