bicycle racing was a popular sport in the 1880s and 1890s.
Explanation:
As a result of stating that "7,000 people watched the night Frankie Nelson set her 18-hour record”, the writer is trying to make it known that a lot of people were interested in watching the event.
Therefore, the thing that most develops the central idea is that bicycle racing was a popular sport in the 1880s and 1890s
