Which retail innovation first introduced the algorithmic 'customers who bought this also bought' recommendation system that transformed how readers discover new books?

In the ever-evolving world of book retail, innovations have transformed how readers discover and purchase literature. From local bookshops to global online platforms, the business of selling books has undergone remarkable changes. This poll tests your knowledge of a significant retail innovation that revolutionized the book industry and changed reading habits worldwide.

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Barnes & Noble's 'Discover Great New Writers' program (1990)
Amazon's collaborative filtering technology (1998)
Borders' 'Original Voices' customer preference tracking (1994)
Book-of-the-Month Club's personalized selection system (1989)