Which linguistic innovation most dramatically improved retail chatbots' ability to understand context and nuance in customer queries after 2018?

AI-powered retail chatbots have transformed customer service by integrating sophisticated linguistic capabilities. But how well do you know the language technology behind these virtual shopping assistants? This poll tests your knowledge of the linguistic innovations that power modern retail chatbots and how they've evolved to understand and respond to natural language. See if you can identify the key linguistic breakthrough that revolutionized retail chatbot capabilities in recent years.

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Transformer-based language models with bidirectional attention mechanisms
Rule-based grammatical parsers with sentiment analysis
Statistical machine translation with n-gram processing
Recursive neural networks with dependency parsing