Which iconic album was first released with an interactive zipper on its cover that could actually be unzipped?

The music industry has seen numerous creative packaging designs that have become as iconic as the music itself. From gatefold sleeves to special edition box sets, album packaging has evolved into an art form that enhances the listening experience. This poll tests your knowledge of a groundbreaking packaging innovation that changed how consumers interacted with physical music products and became a cultural phenomenon in its own right.

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The Rolling Stones' 'Sticky Fingers' (1971)
The Beatles' 'Sgt. Pepper's Lonely Hearts Club Band' (1967)
Pink Floyd's 'The Dark Side of the Moon' (1973)
Led Zeppelin's 'Physical Graffiti' (1975)