Which line can be seen in a 3D or plan view and is also used for dimensions and leader lines?

A solid line is indeed the correct choice for representing dimensions and leader lines in both 3D and plan views in technical drawings. Solid lines are fundamental to creating clear and precise representations of objects, allowing for accurate measurements and annotations. They convey the actual physical edges or outlines of features, enabling designers and builders to interpret the drawings correctly.

In contrast, dashed lines typically represent hidden or obscured features, indicating elements that are not visible in the current view but are still important for understanding the context of the design. Ghost lines are often used to show alternate positions or configurations of elements that may not be in the standard view, while break lines indicate a discontinuity in the drawing, such as where an object has been cropped or omitted for clarity. These lines serve specific purposes but do not fulfill the requirement for dimensions and leader lines the way solid lines do.