What system did the EAC replace?

The correct answer indicates that the EAC, or Exchange Admin Center, was developed to serve as a comprehensive management interface for Exchange environments, effectively replacing both Exchange Management Console (EMC) and Exchange Control Panel (ECP).

The EMC was traditionally used for managing Exchange servers and offered a rich set of features for administrators. However, as needs evolved towards a more web-based and user-friendly interface, the ECP was introduced to streamline some management tasks, particularly those related to user mailboxes and client access.

Ultimately, the EAC combines the functionality of both the EMC and ECP into a single, modern interface that supports a broader range of management tasks and is designed for ease of use and efficiency. This unification helps to provide a more seamless experience for administrators who previously had to navigate two different tools to manage Exchange. Thus, the EAC is the system that replaced both of these previous console types.