To determine the effectiveness of the two sentences, we need to analyze their content and impact.
The first sentence presents a fact about the volume of book purchases, which highlights the popularity of books. The second sentence contrasts this by emphasizing the small financial return that authors receive from these sales, potentially sparking interest in the economic aspect of authorship.
If we consider effectiveness in terms of presenting a clear and compelling contrast between book sales and author profits, the second sentence might be seen as more effective because it gives insight into the disparity faced by authors.
Therefore, the response could be: The second is more effective.