What event marks a turning point in Denny's racing career?

B is the correct answer because Denny's participation in a significant racing competition represents a pivotal moment in his racing career. This event showcases his skills and determination on a larger stage, elevating his profile as a racer. It serves as a catalyst for changes in his career trajectory, leading to new opportunities and challenges. This participation not only highlights his talent but also reinforces the themes of perseverance and ambition that run throughout the narrative.

In contrast, while the other options feature events that relate to Denny's racing journey, they do not encapsulate the same level of transformative impact. His first loss in a major race may affect his mindset, but it does not signal a turning point in his career. Retirement from racing, while significant, represents an endpoint rather than a moment of growth or change. The acquisition of a new racing car might enhance his performance but doesn't inherently mark a shift in his career direction. Thus, participation in a significant racing competition is the event that truly signifies a turning point for Denny.