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

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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 refrigerators 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.
The method of salting food______.

选项 A、was not used in the past
B、involves the use of chemicals
C、is not liked by most people
D、is no longer used by hunter

答案B

解析 根据最后一段第四句“Other chemicals besides salt are used in preserving food.”可知,盐中含有的一些化学物质被用来保存食物。故选B。
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