What Is the Meaning of the Solid Lines Connecting the Boxes

What is the meaning of the solid lines connecting the boxes on an organization chart?
They identify the relationship of the important staff departments.
They identify the level of specialization within the organization.
They identify the reporting relationship, or chain of command, within the organization.
They identify the relationship between the processes in the flow of materials/services.
They identify the products or services available from the organization.