The text is for questions 14 - 16.

    Fog or mist is cloud of condensed water vapor in the form of water droplets or ice crystals, suspended in the atmosphere just over the surface of the earth. In cities and industrial areas, fog often combines with smoke to produce the mixture called smog.

   Meteorologically, fog can be classified into four general types according to the mechanism by which it is formed: advection, radiation, upslope, and precipitation. Advection fog is formed whenever a current of relatively warm, moist air passes over a colder body of land or water. Fog of this type is frequent in the winter when snow is on the ground. It is also common over the ocean, as in the North Atlantic when winds blow across the warm Gulf Stream and reach the cold Labrador Current.

    Radiation fog, formed only over land, is caused by the cooling of the earth by radiation. At night, radiation lowers water temperature comparatively slowły, but land cools rapidly, becoming cooler than the air above it, consequently, a fog is formed. Such fog is seldom thick and usually "burns off" in the morning.

    Upslope fog is formed when air is evenly cooled by its rising and expanding, as when a wind flows up a mountain slope.

    Precipitation fog may form during a snowstorm or rainstorm, if the snow or rain passes through a layer of air that is cooler than the precipitation. Fog of this kind frequently occurs during the passage of warm fronts and cold fronts, when the surface air is markedly different in from the upper air.

Why is the text written?