The correct answer is D. Total sale price of the books sold.
Royalty is a payment made to the copyright holder of a work for the use of that work. The amount of royalty is usually based on a percentage of the sale price of the work. In the case of books, the royalty is typically paid to the author or publisher.
The other options are incorrect because they are not based on the sale price of the books. Option A, number of books published, is not a good measure of the value of the work because it does not take into account the price of the books. Option B, number of books sold, is a better measure of the value of the work, but it is still not perfect because it does not take into account the price of the books. Option C, total cost of books published, is not a good measure of the value of the work because it includes the cost of production, which is not directly related to the value of the work.