Which type of pressure system is characterized by descending air?

A high pressure system is characterized by descending air. This occurs because as air cools and becomes denser, it begins to sink. In a high pressure system, the descending air compresses and warms up, which often leads to clearer skies and more stable weather conditions.

High pressure systems are associated with fair weather as they inhibit cloud formation and precipitation. When air descends, it tends to spread out at the surface, leading to diverging winds that usually result in more stable atmospheric conditions.

In contrast, low pressure systems are associated with rising air, leading to cloud formation and precipitation. Dynamic pressure systems and stable pressure systems aren't standard classifications for describing how air moves, but the primary defining feature of a high pressure system is indeed the descent of air. This makes the high pressure system the correct answer to the question.