An air mass is a large body of air with?

The correct answer highlights that an air mass is characterized by having the same temperature and humidity. Air masses originate from consistent areas of the Earth's surface, such as over oceans or large landmasses, which allows them to acquire uniform temperature and humidity properties.

Temperature within an air mass is essential because it affects the air's ability to hold moisture; warmer air can hold more water vapor than cooler air. Humidity is equally important as it influences various weather patterns, precipitation types, and overall atmospheric stability. An air mass can cause different weather conditions based on its moisture content and temperature.

In the context of the other answer options, while temperature and pressure tend to correlate within a specific air mass, they do not define it as effectively as temperature and humidity. Additionally, it is not essential for the pressure to remain consistent within an air mass as pressure can vary with height and over time as weather systems move. Thus, while the air masses might have similar pressure in a general sense, it is the temperature and humidity that are critical for classifying them.