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. However, Ed has to guard 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 is prepared for the frost . 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 around 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 taken in by the fruit and keeps its temperature at a safe level. Ed has effectively used this method to save many orange crops. But Ed still faces difficulties. The trees must 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 thicker layer of ice that will break the tree's 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 calculate  when the temperature will drop below freezing. The computer can correctly decide the quantity of water to be used and how frequently(  ) the trees should be watered. Ed finds looking after his orange trees a lot easier with the help of a computer, and, his customers will have the benefits  of computer--age oranges. The passage is mainly about  _  .
a farmer expert cares for his orange trees the different uses of computers growing oranges in Florida's changeable weather different ways of frost protection