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  3. Food which is kept too long decays because it is attacked by yeasts(酵母菌)，moulds (霉) and bacteria(细菌). The canning process, howev

Food which is kept too long decays because it is attacked by yeasts(酵母菌)，moulds (霉) and bacteria(细菌). The canning process, howev

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问题    Food which is kept too long decays because it is attacked by yeasts(酵母菌)，moulds (霉) and bacteria(细菌). The canning process, however, seals the product in a container so that no infection can reach it, and then it is sterilized(消毒)by heat. Heat sterilization destroys all infections present in food inside the can.  No chemical preservatives are necessary, and properly canned food does not deteriorate during storage.
   Today vegetables, fish, fruit, meat and beer are canned in enormous quantities. Foods that were previously seasonal may now be eaten at any time, and strange foods are available far from the countries where they are grown. The profitable crops many farmers now produce often depend on the proximity of a canning factory.
   The first stage in the canning process is the preparation of the raw food. Diseased and waste portions are thrown away; meat and fish are cleaned and trimmed; fruit and vegetables washed and graded for size. The jobs are principally done by machine.
   The next stage, for vegetables only, is blanching. This is immersion(浸洗) in very hot or boiling water for a short time to remove air and soften the vegetable. This makes it easier to pack into cans for sterilization. Some packing machines fill up to 400 cans a minute. Fruit, fish and meat are packed raw and cold into cans, and then all the air is removed. When the cans are sealed, the pressure inside each can is only about half the pressure of the outside air. This is" vacuum" packing.
   During the sterilization process which follows, the cans are subjected to steam or boiling water, with the temperature and duration varying according to the type of food. Cans of fruit, for example, take only 5-10 minutes in boiling water, while meat and fish are cooked at higher temperature for longer periods . After sterilization, the cans are cooled quickly to 32℃, to prevent the contents from becoming too soft.
   The final stage before dispatch to the wholesale or retail grocer is labeling, and packing the tins into boxes. Nowadays, however, labeling is often printed on in advance by the can maker and no paper labels are then required.
Vacuum packing is to ______.
选项 A、immerse food in very hot or boiling water
B、sterilize food
C、remove air from the cans
D、subject food to steam or boiling water
答案C
解析 这一题要求我们对细节认真阅读后再作出判断。文中第四段详细介绍厂真空包装。各种食品装入罐中后，将所有空气抽出，使外部压强高于内部压强。这样就是所谓真空包装了。所以最合适的答案应为C项。
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