Which type of line is characterized by heavy unbroken lines?

The correct answer is that heavy unbroken lines are characterized as object lines in technical drawings or plans. Object lines are used to represent the outlines of visible objects or features in a design, clearly indicating the shapes and boundaries of physical elements. Their solid and prominent appearance ensures that essential components are easily recognizable and distinguishable from other types of lines that may convey different information, such as hidden or phantom lines.

In this context, object lines play a crucial role in conveying the primary details of the drawing, allowing anyone interpreting the diagrams to understand the main structures and components without confusion. Their weight and continuity facilitate clarity and emphasize the significance of the depicted elements.