Final answer:
Cisco DNA Center is the enterprise management platform designed to support Cisco SDA with a centralized controller and graphical user interface.
Step-by-step explanation:
The enterprise management platform that is specifically built to support Cisco Software-Defined Access (SDA), featuring a centralized controller and GUI, is Cisco DNA Center. Cisco Network Assistant and Cisco PI are network management tools, but they do not offer the same level of integration with Cisco SDA as Cisco DNA Center does. Cisco IOS 15 is an operating system for Cisco routers and switches, and it is not a centralized management platform. Cisco DNA Center provides an intuitive interface for network management, automation, assurance, and security, and it is central to Cisco's intent-based networking approach.