Answer: Delta

Delta Lake tables are stored in the Delta format, which is built on top of Parquet files but includes additional metadata and transaction logs. While Parquet is the underlying storage format for data files, Delta is the complete format that includes: 1. **Parquet data files** - for storing the actual data 2. **Transaction log** - for ACID compliance and versioning 3. **Checkpoint files** - for optimizing transaction log reads 4. **Metadata** - for schema enforcement and evolution The correct answer is D (Delta) because Delta Lake tables use the Delta format, which is more than just Parquet files - it's a complete storage layer with transactional capabilities.

Author: Keng Suppaseth