Answer:
The article talks mainly about B. the stables where professional sumo wrestlers train, eat, and sleep.
Step-by-step explanation:
The given options present various aspects of Japanese culture and history. While A, C, and D touch upon samurai warriors, the prominence of sumo wrestling as a sport, and religious harvest rituals respectively, option B specifically mentions "stables where professional sumo wrestlers train, eat, and sleep." The detailed focus on the life and routines of sumo wrestlers within their training environment suggests that the main subject of the article is centered around the intricacies of these stables and the lives of the sumo wrestlers therein.