Final answer:
According to systems theorists, an understanding of social systems and large bureaucracies is necessary for understanding how an organization's departments interrelate.
Step-by-step explanation:
The type of skill necessary for understanding how an organization's departments interrelate, according to systems theorists, is an understanding of social systems and large bureaucracies. Systems theorists view society as having a system of interdependent inherently connected parts. They believe that organizations are complex systems with interconnected departments that influence and depend on each other.