Which retail innovation did Amazon Prime Day pioneer that has now been widely adopted by other major retailers?

Amazon Prime Day has become one of the most significant shopping events in e-commerce history. What began as a celebration of Amazon's anniversary has transformed into a global shopping phenomenon that influences retail strategies worldwide. This trivia question tests your knowledge about how this shopping festival has changed the retail landscape and created a new model for customer engagement and sales acceleration.

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Creating a members-only shopping event that drives subscription value
Introducing doorstep delivery within 24 hours of purchase
Establishing the first major post-holiday season clearance sale
Launching the concept of flash sales with countdown timers