Fog Often Lingers in River Valleys Because

Fog often lingers in river valleys because

A) the water in the river cools off faster at night than the land does.
B) cold air rises from low areas such as river valleys.
C) some evaporation may occur from the river,thereby supplying moisture to the cooler atmosphere.
D) water vapour drains downslope into the valley.
E) sublimation chills the valley.