The correct answer is D. Damping.
Damping is a technique used to reduce vibration and oscillations in mechanical systems. It is not a critical feature in PC CAD software, as it is not necessary for the creation or editing of drawings.
Crosshatching is a technique used to fill in areas of a drawing with a pattern of lines. It is a useful feature for adding visual interest and clarity to drawings.
Layering is a technique used to organize different elements of a drawing into separate layers. This can be helpful for keeping track of complex drawings and for making changes to individual elements without affecting the rest of the drawing.
Drawing/editing is the core functionality of PC CAD software. It allows users to create and edit drawings of two-dimensional or three-dimensional objects.
Therefore, the correct answer is D. Damping.