Which major music retailer first implemented dynamic pricing algorithms for digital music in 2011, causing a revolution in how music prices fluctuate based on demand?

The music retail landscape has evolved dramatically in the digital age. One of the most significant innovations in music retail has been the implementation of sophisticated pricing strategies that respond to market demand. This trivia question explores a pivotal moment in music retail pricing innovation that changed how albums and singles are sold online. Test your knowledge of the business side of the music industry!

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iTunes with its 'Popularity Pricing' system
Spotify with its 'Market-Responsive Purchase Points'
Amazon MP3 with its 'Demand-Shift Pricing'
Bandcamp with its 'Artist-Controlled Variable Pricing'