Which innovative packaging approach first popularized the concept of 'bite-sized' language learning that has now become standard in most language learning apps?

Packaging design in the language learning industry has evolved dramatically over the decades. From physical dictionaries and textbooks to digital apps and immersive experiences, the way language learning products are packaged and presented to consumers reflects changing educational philosophies and technological capabilities. This poll tests your knowledge about a groundbreaking packaging innovation that transformed how people perceive language learning products.

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Pimsleur's color-coded audio cassettes (1970s) that divided learning into 30-minute sessions
Rosetta Stone's yellow box design with level-based CD-ROMs that visually represented learning progression (1990s)
Duolingo's gamified 'skill tree' interface with short, 5-minute lessons (2011)
Berlitz's pocket-sized phrasebooks with tear-out vocabulary cards (1980s)