The correct option is Relational database.

Relational database systems organize data into tables that use named columns and rows so queries can reference fields directly and return results efficiently. They provide a fixed schema, indexing, and SQL query engines that make retrieval and joining of related records fast and predictable.

Relational database designs also support constraints and transactions which help maintain data integrity when multiple operations update related rows. Those characteristics make them the right match for an operational store that relies on named fields and row relationships for querying.

Plain text file is wrong because plain text lacks structured columns and rows and does not provide indexing or query capabilities that make retrieval efficient.

Spreadsheet is wrong because although it uses a rows and columns layout it is not a database engine designed for efficient, large scale querying or relational joins and it lacks the transactional and indexing features of a relational database.

Document database is wrong because document stores save semi structured documents such as JSON and they organize data around documents rather than fixed tables of named columns and rows. That model is optimized for flexible schemas and nested data rather than traditional relational queries.

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