The correct option is Azure Stream Analytics.

Azure Stream Analytics is a purpose built, real time analytics service that ingests and analyzes high volume event streams with low end to end latency. It supports SQL like streaming queries for on the spot computations and routing, and it integrates directly with ingestion sources such as Event Hubs and IoT Hub and with sinks like Power BI and Cosmos DB.

Azure Event Hubs is a high throughput ingestion and event streaming platform but it does not perform the real time analytics itself. It is commonly used to feed analytics services such as Azure Stream Analytics.

Azure Synapse Analytics is a unified analytics and data warehousing platform that focuses on large scale batch and interactive queries and big data processing. It can handle streaming scenarios with other components but it is not the specialized low latency stream analytics engine described in the question.

Azure Cosmos DB is a globally distributed NoSQL database that provides low latency storage and querying for structured data. It is not intended as a real time stream processing and analytics service for high throughput event streams.

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