Step 1: Understanding the Concept:
This question requires extracting a specific factual detail provided in the comprehension passage regarding Subbu's writing.
Step 2: Detailed Explanation:
The passage explicitly mentions that Subbu wrote a "sprawling novel Thillana Mohanambal."
It further adds: "He quite successfully recreated the mood and manner of the Devadasis of the early 20th century."
This indicates that the primary subject matter of his novel was the culture and lifestyle of the Devadasis during that historical period.
Step 3: Final Answer:
The correct option is (B).