What yields the classification of an air mass based on its source region?

The correct choice is based on the understanding that air masses are classified according to their source regions, which are specific areas on the Earth's surface where the air masses originate. The characteristics of an air mass, including temperature and humidity, are strongly influenced by the geographic and environmental conditions of these source regions. For instance, an air mass that forms over a cold ocean will generally be colder and more humid than an air mass that forms over a warm desert.

While temperature and humidity are significant factors in describing the properties of an air mass, it is the source region that ultimately determines those properties and thus leads to their classification, such as maritime or continental, tropical or polar. Therefore, recognizing the source region is fundamental in understanding the characteristics and behaviors of the air masses. This classification system allows meteorologists to predict weather patterns and changes based on the interaction of different air masses.