On a hydraulic or pneumatic diagram, local areas are outlined by which of the following?

The correct choice indicates that solid lines are used to outline local areas in hydraulic or pneumatic diagrams. Solid lines serve as clear and definitive boundaries that help to delineate different components, sections, or functional areas within the diagram. This straightforward representation enhances the clarity of the diagram, allowing for easy identification of critical parts and their relationships to each other.

In these types of diagrams, solid lines represent physical boundaries or connections without ambiguity, making them essential for conveying the layout and operations of hydraulic or pneumatic systems effectively. This is particularly important in technical contexts where precision and clear communication are vital for interpretation, troubleshooting, and maintenance of the systems depicted.