Which of the following is a key feature of a relational database?

It is designed for highly available systems that should provide a consistent, high$-$quality experience for all users globally.

It has high scalability and performance that can enable almost unlimited growth.

It has flexible data models that make it easy to store and combine data of any structure and allow dynamic changes to the schema.

It uses primary keys and foreign keys as a means to provide efficient access to data and is supported directly in the database rather than maintained in the application code.