Which Azure service is used for building conversational AI applications and chatbots?

Correct answer: Azure Bot Service with Language Understanding (LUIS)

Option A is correct because Azure Bot Service is Microsoft's dedicated platform for building, connecting, and managing intelligent chatbots, and Language Understanding (LUIS) provides the natural language processing capability that allows bots to interpret user intents and entities in conversational scenarios. Option B is incorrect because Azure Data Factory is a cloud-based ETL and data integration service used for orchestrating data pipelines, not for building chatbots or conversational interfaces. Option C is incorrect because Azure Event Hubs is a high-throughput data streaming and event ingestion service designed for telemetry and event-driven architectures, not conversational AI. Option D is incorrect because Azure Synapse Analytics is a unified analytics platform for big data and data warehousing, with no native capability for building conversational AI applications.