What combination of air characteristics is defined as 'cool and dry'?

The correct choice, which identifies the combination of air characteristics defined as 'cool and dry,' refers to stable air. In meteorology, stable air is characterized by its lack of vertical motion and tends to remain at a consistent temperature. Cool air, particularly when it is dry, is less likely to rise as warmer air does, contributing to stability in the atmosphere.

Stable air typically results in clear skies and calm weather conditions, as it suppresses convection and the development of clouds. This stability prevents moisture from accumulating, leading to a dry atmosphere. In contrast, unstable air is often warmer and more humid, capable of rising rapidly, which can lead to cloud formation and turbulent weather.

Thus, recognizing stable air as 'cool and dry' is foundational in understanding how different atmospheric conditions affect weather patterns. The characteristics of moist air would suggest humidity, which directly contradicts the notion of being dry, while high pressure air can sometimes encompass both stable conditions and moisture; however, it does not exclusively define the 'cool and dry' aspect as clearly as stable air does.