Final answer:
A large body of air with nearly uniform properties of temperature, humidity, and stability is called an air mass. This concept is key in determining weather patterns and is different from monsoons, fronts, and low-pressure systems which involve movement and interaction between different air masses or directional wind changes.
Step-by-step explanation:
A large body of air near the surface with nearly uniform properties (temperature, humidity, and stability) is called an air mass. Air masses are significant in determining weather, as they often cover significant portions of continents or oceans. When these air masses move and meet different air masses, the interaction can lead to weather events such as low-pressure systems, which give rise to clouds and precipitation, or fronts, which can cause sudden changes in weather conditions.
Monsoons are seasonal winds and are best known for causing heavy rainfall in certain parts of the world, like South Asia. They are not characterized by uniform properties over an area like air masses but instead are a seasonal phenomenon resulting from a reversal of wind direction. Therefore, the correct answer to the question is d. an air mass.