An air mass changes
a. the rotation direction of cyclones
b. weather that is hundreds of kilometers away from it
c. the weather of the area over which it moves
d. the elevation of underlying areas

The correct answer is C, as an air mass changes the weather of the area over which it moves.

An air mass is defined as a large portion of air, with a horizontal extension of several hundred kilometers, whose physical properties, especially temperature, moisture content and vertical temperature gradient, are more or less uniform.

Between two air masses fronts are formed, which can have different temperatures.

The cold front is a band of instability that occurs when a mass of cold air approaches a hot air mass. The cold air, being more dense, generates a "wedge" and gets under warm and less dense air.

The cold fronts move quickly. They are strong and can cause atmospheric disturbances such as thunderstorms, squalls, tornadoes, strong winds and short snowstorms before the cold front passes, accompanied by dry conditions as the front advances.

The warm front is the front of a warm air mass that moves to replace a cold air mass. Generally, with the passage of the warm front the temperature and humidity increase, the pressure drops and although the wind changes it is not as pronounced as when a cold front passes.

An occluded front is formed when a slower moving hot front is followed by a cold front with faster displacement. The cold wedge-shaped front reaches the hot front and pushes it upwards. The two fronts continue moving one behind the other and the line between them is what forms the occluded front.

Finally the stationary front is a limit between two air masses, of which none is strong enough to replace the other.