To compare the effectiveness of the two sentences, we need to consider what each sentence communicates. The first sentence highlights the large volume of book purchases, which underscores the popularity of books. The second sentence points out the disparity between the number of books sold and the profits received by authors, highlighting an important issue in the publishing industry.
In terms of effectiveness, both sentences serve different purposes but complement each other. The first establishes the context of book sales, while the second reveals the economic realities faced by authors.
Given this analysis, the most accurate response would be: They are equally effective.