Which line is a heavy solid line used to represent the outline of an object in a drawing?

The correct choice identifies the heavy solid line known as the object line, which is essential in technical drawings. This line is used to define the visible edges of an object, clearly outlining its shape and structure. The thickness of the object line helps distinguish it from other types of lines present in the drawing, which serve different purposes. By using a heavy solid line for the object outline, it allows anyone reading the drawing to easily identify and understand the primary form of the object being represented.

Other line types, such as hidden lines, construction lines, and center lines, have distinct roles within the drawing but do not function as outlines for the object. Hidden lines illustrate edges that are not visible from the current viewpoint, while construction lines provide a guide during the drawing process and are often lighter in weight. Center lines indicate symmetry or the axis of an object, but they also do not serve as the object's boundary outline.