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、阅读理解（本大题共5小题，共0分） A Farmer Ed Rawlings smiles as he looks at his orange trees. The young oranges are growing well in Florida's weather. Warm sunshine and gentle rains, along with Ed Rawlings' expert care, will produce a good crop of oranges this year. But Ed has to fight against Florida's changeable winter weather. In January and February, temperatures can destroy Ed's entire orange crop. Having farmed in Florida for the past 35 years, Ed Rawlings is prepared for the frosts (霜). When temperatures drop below freezing, Ed tries to save his crop by watering his orange trees. The water freezes and forms a thin layer (层) of ice on the trees. Strange as it may sound, this thin layer of ice actually keeps the fruit warm. What happens is simple. When the trees are watered, the water loses heat and becomes ice. The warmth of the heat it loses is sucked in by the fruit and keeps its temperature at a safe level. Ed Rawlings has effectively used this method (方法) to save many orange crops. But Ed still faces some difficulties. The trees should be watered at the exact moment the temperature drops to the freezing point. Also, just the right quantity of water must be used. Too much water can form a thick layer of ice that will break the trees' branches. Another difficulty is that wind blows away the heat. So Ed has to worry about not only when but also how often his trees should be watered, and how much water should be used. | 
