The "rain" of the proverb "Three days of heavy fog, there will be heavy rain" is mostly caused by A. Convective rain B. Typhoon rainstorm C. Topographic precipitation D.

Test analysis:

Fog is fog. The fog lasted for three days, indicating that the warm and humid airflow was particularly strong and the water vapor content in the atmosphere was large. The stronger the warm and humid airflow, the greater the rain when the cold air arrives. Therefore, the proverb "three days of fog, there will be heavy rain." When cold and warm air meet and rain, it is frontal rain, D right. Convective rain means that when the ground temperature is high and the water vapor rises strongly, the altitude rises and the temperature drops, causing rain through condensation, and there will be no foggy weather. A is wrong. Typhoon rain without foggy weather, b wrong. Topographic precipitation is rainfall in which water vapor is lifted by topography and the temperature drops with the elevation. The ground temperature is higher than that at high altitude, so there is no inversion, fog and C error.