Many residents of Calovia are committed to using products containing recycled materials. Soon these consumers will get help in identifying such products from a book being published by the Calovian government. The book offers a comprehensive listing, by product type and brand, of goods sold in Calovia that contain recycled material. Therefore, publication of the book will almost certainly increase the use of products containing recycled materials in Calovia.

Which of the following, if true, most strengthens the argument?

【选项】Many manufacturers of products that contain recycled materials vary the proportion of recycled materials in those products in response to changes in price and availability.