B. by building the text around evidence in the form of supporting details
The author of a text develops central ideas primarily by building the text around evidence in the form of supporting details. This is option B. By providing strong evidence and supporting details throughout the text, the author establishes and develops the central ideas. This helps to convince the reader and provide a clear understanding of the main points being conveyed. While options A, C, and D may play a role in organizing and clarifying the overall structure of the text, they do not specifically address how the central ideas are developed.