Which of the following is NOT a type of matter where static charges can build up?

The correct answer identifies metals as a type of matter where static charges typically do not build up. Metals are excellent conductors of electricity, allowing charges to flow freely and be easily dissipated rather than accumulating. When static electricity is generated, it usually occurs in insulating materials or non-conductors, where the movement of electrons is restricted.

In contrast, the other options represent materials that can easily accumulate static charges. For instance, pipes and vents can be made of plastic or used in a way that creates friction, allowing charge accumulation. Dust particles are insulators and can also build up static charges through friction with surfaces. Moving machine parts, particularly if made of non-conductive materials or treated in a certain way, can generate static electricity through friction and contact as they rub against each other.

Thus, understanding the electrical properties of materials highlights why metals are not typically associated with the buildup of static electricity.