The correct answer is Azure Databricks.

Azure Databricks provides a fully managed serverless Apache Spark runtime that is optimized for large scale analytics and for training machine learning models. It integrates with Azure services and supports the Cosmos DB Spark connector so you can process and train models directly against data stored in Azure Cosmos DB.

Azure Functions is a serverless compute service for event driven and short lived workloads and it does not provide a managed Apache Spark runtime for large scale analytics or model training.

Azure Machine Learning is a managed service for building, training, and deploying machine learning models but it does not deliver a native fully managed serverless Apache Spark runtime as Databricks does.

Azure HDInsight offers managed Hadoop and Spark clusters but it relies on provisioned clusters rather than a fully managed serverless Spark runtime and it is not the service referenced by the question.

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