If warm, moist air flows over cold land, what is the correct explanation for fog formation?

Correct answer: Warm, moist air cools by contact and reaches its dew point

Correct answer: A. The moving air already contains moisture because it is warm and humid. When it passes over a colder land surface, heat flows from the air toward the ground. The lower part of the air mass cools by contact with the surface. If it cools to the dew point, the air becomes saturated and some water vapour condenses on tiny particles in the air, producing suspended droplets and fog. This type is commonly called advection fog because moist air is transported over a colder surface. B is wrong because land does not destroy water vapour; it removes heat from the air. C is wrong because cooling does not automatically make air dry, and frost requires deposition as ice on a sufficiently cold surface. D is the opposite of the process: the cold surface is what supplies the cooling needed for fog. Memory cue: warm moist air plus a cold surface plus contact cooling equals fog, provided saturation is reached.