Final answer:
The correct option for a beneficial function of enterprise application integration (EAI) is that it provides a new software layer to connect previously isolated systems, enabling better communication and data sharing.
Step-by-step explanation:
The beneficial function of enterprise application integration (EAI) among the options provided is C: It connects system "islands" via a new layer of software. This allows previously disparate and independent systems to communicate and share data more effectively. EAI serves to integrate the various enterprise systems and applications, thereby enabling a more streamlined, efficient, and cooperative IT environment. By doing so, it simplifies processes, improves real-time information access, and enhances organizational agility.