Which retail innovation first made religious texts widely affordable to the average person in the early 19th century?

Religious texts are some of the most enduring 'products' in human history, with distribution and marketing strategies that have evolved over centuries. This trivia question explores a revolutionary retail innovation that dramatically changed how religious texts were distributed and consumed in the modern era. Test your knowledge of this intersection between spiritual content and product distribution!

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The American Bible Society's steam-powered printing press system (1816)
Oxford University Press's subscription model (1823)
Thomas Nelson's leather-bound portable editions (1835)
Vatican Library's public domain religious text repository (1808)