Which innovative language learning product marketing approach first successfully leveraged the concept of 'spaced repetition' to revolutionize vocabulary acquisition?

In the world of language and linguistics, product marketing represents a fascinating field of study. Companies carefully craft their messaging to connect with consumers on both conscious and subconscious levels. This poll tests your knowledge of how language innovation has shaped modern product marketing within the linguistics industry itself. Can you identify which revolutionary approach to language learning truly disrupted the market?

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Duolingo's gamification system (2011)
Rosetta Stone's immersion method (1992)
SuperMemo's algorithm-based learning (1987)
Babbel's situational learning approach (2007)