Final answer:
The statement is true; the Rib command in CAD software requires pre-existing geometry, such as a sketch, to define the path and placement of the reinforcing feature that it creates.
Step-by-step explanation:
The statement that the Rib command requires pre-existing geometry and cannot be added alone is true. In CAD (Computer-Aided Design) software, the Rib command is used to create a feature that reinforces or strengthens the structure of a part. It does this by adding material in a specific direction while keeping a consistent thickness.
The Rib command is typically dependent on existing geometry to define the path and the surfaces to which the rib will be added. Without pre-existing geometry to define these parameters, the rib feature cannot be established. In practice, you would select a sketch that outlines the rib's placement and trajectory, and then use the Rib command to extrude this sketch perpendicular to the sketch plane, thereby creating the added structural feature.