Which revolutionary shopping feature did Amazon patent in 1999 that became standard across e-commerce and caused significant controversy?

E-commerce has transformed retail with innovations that make shopping more convenient and personalized. Among the major players, Amazon has been a pioneer in patenting technologies that changed how we shop online. This trivia question tests your knowledge of one of Amazon's most significant and controversial patents that fundamentally altered the e-commerce landscape and customer purchase journey.

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1-Click purchasing
Product recommendation algorithm
Customer review system
Prime subscription model