Final answer:
The main purpose of the passage is to analyze the strategies of Thoroughbred horseracing as they relate to journalistic coverage, suggesting Option D as the correct answer.
Step-by-step explanation:
To determine the main purpose of the passage, one must consider what the author is trying to achieve with their writing. Based on the information provided, the passage does not seem to focus on classifying types of horses, narrating a specific event, challenging the treatment of Thoroughbred horses, or explaining the complexities of riding such horses. Instead, the passage appears to discuss and analyze the horserace coverage and might likely be aiming to analyze strategies in Thoroughbred horseracing as they relate to reporting and informing the audience. Therefore, the most suitable answer would be to analyze the strategies of Thoroughbred horseracing (Option D).