Which retail innovation, introduced by Clarence Saunders in 1916, fundamentally changed how Americans shopped and became the standard model for grocery stores worldwide?

Throughout history, certain retail innovations have fundamentally transformed how we shop and consume. These breakthroughs didn't just change business—they altered society and culture. This trivia question focuses on one of the most significant but often overlooked retail innovations that revolutionized consumer behavior in the early 20th century. Test your knowledge of retail history with this challenging question!

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Self-service shopping (Piggly Wiggly stores)
Shopping cart (invented for Humpty Dumpty stores)
Checkout counter with conveyor belt
Loyalty card program (S&H Green Stamps)