Which retail innovation, introduced in 1916, revolutionized shopping by allowing customers to select their own merchandise without clerk assistance for the first time?

The history of retail has seen dramatic transformations that shaped how we shop today. From small general stores to massive department stores, mail-order catalogs to e-commerce giants, retail innovation has consistently responded to societal changes and technological advancements. This trivia question focuses on a pivotal moment in retail history that fundamentally changed the shopping experience and created a foundation for modern retail strategies.

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The self-service grocery store (Piggly Wiggly)
The department store with multiple floors (Marshall Field's)
The mail-order catalog system (Sears Roebuck)
The shopping mall concept (Country Club Plaza)