The correct answer is C because Delta Lake is the open-source storage layer that provides reliability and structure for data lakes. Delta Lake brings ACID transactions, scalable metadata handling, and batch/streaming support to data lake storage, which are core capabilities behind the lakehouse architecture. MLflow is for machine learning lifecycle management, Apache Spark is a distributed processing engine, and Databricks SQL is a Databricks product for SQL analytics, not the open-source storage project described.

Official documentation extract used: Databricks states that Delta Lake is ''open source software'' and provides ''ACID transactions and scalable metadata handling.''