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Cities are generally warmer than the surrounding countryside, a phenomenon known as the urban heat island. A. In the countryside, much solar energy is used in evaporation, but in the city this energy builds up as heat. B. Increased industrial and urban development has also increased average levels of humidity over the last century. C. Pollution from cars and factories helps increase the amounts of fog and precipitation that occur in cities. D. The urban heat island is strongest in the summer, when the days are long and the sunlight is intense. E. Heat and air are trapped in the irregular spaces between buildings, which creates the atmospheric conditions that result in storms and winds. F. Country breezes blow pollutants put from the cities into the surrounding countryside.