Answer:
C. A mass of air that is similar in temperature and humidity
Explanation:
An "air mass" refers to a big volume of air that is characterized by having similar or uniform "temperature" and "humidity" (moisture). They come from different source regions, thus they are classified accordingly.
The "cold air masses" come from the polar areas while the "warm air masses" come from the tropical areas. An air mass may cause a storm, for example, when an air mass moves to a new region and confronts another air mass there with a different humidity and temperature.
