What disaster recovery model involves having a database server in sync with a primary data center but not fully operational?

The correct answer, which involves maintaining a database server that is in sync with a primary data center but not fully operational, refers to a warm site. In a warm site disaster recovery model, systems and data are kept up-to-date with the primary site, allowing for a quicker recovery time than a cold site, which is typically not operational and may require significant time to set up. Unlike a hot site, where everything is fully operational and ready to go at a moment's notice, a warm site strikes a balance by being partially ready—meaning it may require some configuration or data restoration to be fully functional in a disaster scenario. Thus, having a database server in sync but not fully operational is characteristic of a warm site, making it the most fitting choice.