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

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 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 in the ground.
    Cooking will usually kill bacteria if the temperature is high enough and 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 cat vegetables, salt be came a needed part of their life. Salt helps to preserve food because it slows or stops bacteria growth. Other chemicals besides salt are used in preserving foot. Some people oppose the use of chemicals in food. They say that these chemicals may harm people if the chemicals can harm bacteria.
This passage is mainly about      .
选项 A、the different ways of preserving food
B、why we must kill tbe bacteria in our food
C、the importance of preserving food
D、how to preserve food by cooking and salting
答案A
解析 本题是关于文章的主旨。主旨题如果出现在最后一题的话，号生多数情况下要从全篇来把握，把每一段的段落主旨加以综合归纳就是全文的主旨。在第一段作者介绍了保存食物的原理，从第二段起开始介绍保存食物的各种方法如：冷冻法、烹饪法、晒干法、盐腌法以及添加化学成分法等等。因此文章的主旨是保存食物的各种方法，答案选A
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