What processes add moisture to unsaturated air?

The correct choice is based on the understanding of how moisture enters the atmosphere and affects unsaturated air. Evaporation plays a crucial role in adding moisture to the air; it occurs when water from surfaces such as oceans, lakes, or vegetation transforms from a liquid state into vapor. This process increases the humidity of the surrounding unsaturated air.

Sublimation, the transition of water from a solid state directly into vapor, also contributes to the moisture content of the atmosphere, especially in cold environments where snow or ice can change directly into water vapor without first melting into liquid water.

Both evaporation and sublimation are essential in processes that provide moisture to unsaturated air, making this choice the most appropriate answer to the question concerning the addition of moisture to the atmosphere.