四级考试阅读主旨题解题技巧实战14

　　But ED has to fight against Floridas changeable winter weather. In January and February, temperature can destroy EDs entire orange crops. Having farmed in Florida for the past 35 years, Ed Rawlings is prepared for the frosts. When temperatures drop below freezing, Ed tries to save his crop by watering his orange trees. The water freezes and forms a thin layer of ice on the trees. Strange as it may sound, this thin layer of ice actually keep 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 sicked in by the fruit and keeps its temperature at a safe level. Ed Rawling has effectively used this method 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.

　　Computer technology may help Ed with some of these worries. With equipment, air and soil temperatures and wind speed can be measured. The information is fed into a computer which can tell when temperatures drop to freezing. The computer can correctly decide the quantity of water to be used and how frequently the trees should be watered. Ed will find looking after his orange trees a lot easier with the help of a computer, and well all have the benefits of computerage oranges.

　　The passage is mainly about_______.

　　A a farmers expert care for his orange trees

　　B the different uses of computers

　　C growing oranges in Floridas changeable weather

　　D different way of frost protection