The correct answer is A federation feature that lets you execute T-SQL queries against external data sources.

PolyBase enables you to define external tables and query data that lives outside the Synapse SQL engine using standard T-SQL. It acts as a federation layer so you can join and query files in blob or data lake storage and remote relational systems as if they were local tables.

A method for compressing stored data to save space is incorrect because PolyBase is about querying and integrating external data and not about data compression. Compression is handled by storage formats and database compression features instead.

BigQuery is incorrect because that is a Google Cloud analytics service and not a capability of Synapse or PolyBase. The option names a different product rather than describing the PolyBase feature.

A real time ingestion pipeline for streaming IoT telemetry is incorrect because PolyBase does not provide streaming ingestion. Real time telemetry ingestion is handled by streaming services and pipelines such as Event Hubs and Stream Analytics or Synapse Pipelines and not by PolyBase.

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