Which innovative product design approach revolutionized language learning apps by introducing 'spaced repetition systems' (SRS) as a core feature for vocabulary retention?

The intersection of language learning and product design has evolved dramatically in recent years. Companies have innovated beyond traditional textbooks and classroom settings, creating technological solutions that adapt to individual learning styles and needs. Test your knowledge about a major breakthrough in linguistic product design that changed how millions approach language acquisition.

This is a live public trivia poll on AIPolls.Net. Vote and see real-time results.

Duolingo's gamification model with streak counters and XP rewards
Anki's algorithmic flashcard system that schedules reviews based on recall difficulty
Babbel's conversation-based approach with speech recognition feedback
Rosetta Stone's immersion method using images without translations