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  3. Centuries ago, man found out that removing moisture from food helps to preserve it, and that the easiest way to do this is to ex

Centuries ago, man found out that removing moisture from food helps to preserve it, and that the easiest way to do this is to ex

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问题    Centuries ago, man found out that removing moisture from food helps to preserve it, and that the easiest way to do this is to expose the food to sun and wind.
   All foods contain water—cabbage and other leaf vegetables contain as much as 92% water, potatoes and other root vegetables 80%, lean meat 70% and fish anything from 80% to 60% depending on how fatty it is. If this water is removed, the activity of the bacteria(细菌) which cause food to go bad is checked.
   At present most foods are dried mechanically. The conventional method of such dehydration (脱水) is to put food in chambers through which hot air is blown at temperature of about 110℃ at entry to about 43℃ at exit. This is the usual method for drying such things as vegetables, minced meat and fish.
   Liquids such as milk, coffee, tea, soup and egg may be dried by pouring them over a heated horizontal steel cylinder or by spraying them into a chamber through which a current of hot air passes. In the first case, the dried material is stripped off the roller as a thin film which is then broken up into small, though still relatively coarse flakes. In the second process it falls to the bottom of the chamber as a fine powder. Where recognizable pieces of meat and vegetables are required, as in soup, the ingredients are dried separately and then mixed.
   Dried foods take up less room and weight less than the same food packed in cans or frozen, and they do not need to be stored in special conditions. For these reasons they are invaluable to climbers, explorers and soldiers in battle, who have little storage space, they are also popular with housewives for it takes so little time to cook them. Usually it is just a case of replacing the dried-out moisture with boiling water.
The chief point of the second paragraph is about ______ .
选项 A、the comparison of lean meat and fish
B、the removal of water in food
C、the water content in food
D、the relationship between water and food
答案C
解析 本题考查主旨题。第三段在讲述各种食物里水的含量，故选C。
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