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  3. To preserve food, the growth of bacteria(细菌) must be controlled. Water, warmth, and food are all needed for bacteria to become s

To preserve food, the growth of bacteria(细菌) must be controlled. Water, warmth, and food are all needed for bacteria to become s

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问题     To preserve food, the growth of bacteria(细菌) must be controlled. Water, warmth, and food are all needed for bacteria to become strong and healthy. Some kinds of bacteria need air, but other kinds grow only when air is absent. Extremes of temperature, either hot or cold, can kill bacteria.
    Before electric ice-boxes were invented, freezing and cooling were limited by the cold climate. In warmer regions, food was cooled by putting it in the shade, in cold water from the well, or in pits(坑) in the ground.
    Cooking will usually kill bacteria if the temperature is high enough and the high temperature lasts long enough. Certain methods of cooking remove water, and this aids in preserving food. Drying is the oldest and most common method of preserving food. Food can be dried by the sun, by heat or by combination of the two.
    Salt was used by many hunting people. When people began to eat vegetables, salt became a needed part of their life. Salt helps to preserve food because it slows or stops bacteria to grow. Other chemicals besides salt are used in preserving food. Some people oppose the use of chemicals in food. They say that these chemicals may harm people if the chemicals can harm bacteria.
What is the passage mainly about?
选项 A、Ways of preserving food.
B、The bacteria in our food.
C、The importance of preserving food.
D、Ways of cooking food.
答案A
解析 主旨大意题。因此文章的主旨是讲述保存食物的不同方法。故选A。
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