Your team manages several petabytes of historical, structured transaction data stored in Apache Avro format...

The correct answer is C because BigQuery external tables allow BigQuery to query data stored in Cloud Storage without loading it into BigQuery managed storage. This directly satisfies the requirement to minimize storage cost and avoid ingestion overhead. Apache Avro is a supported format for analytical workloads, and partitioning by a relevant column improves query performance and cost control when only subsets of the historical data are needed. Option A loads the data into native BigQuery storage, which increases managed storage usage. Option B is unsuitable because Cloud SQL is not designed for petabyte-scale analytical transaction history or machine learning workloads. Option D also loads data into BigQuery, which violates the requirement to avoid loading overhead.