阅读理解 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.
单选题 How can we preserve food according to the first paragraph?
【正确答案】 C
【答案解析】事实细节题。根据文章第一段首句可知，要想保存食物，必须控制细菌的 生长，所以C为正确答案。
单选题 Cooking is an effective way in preserving food because______.
【正确答案】 D
【答案解析】事实细节题。根据文章第三段第一、二句可知，在一定的条件下(即温 度够高、烹饪时间够长)，烹饪法能杀死细菌，因此是一种保存食物的有效方法。
单选题 The method of salting food______.
【正确答案】 B
【答案解析】推理判断题。根据文章最后一段第三、四句“…Other chemicals besides salt are used in preserving food．”可知，除了食盐之外，还有其他的化学物质被用来保存食物。注意，besides为“除……之外，还有”之意，故可推出，腌制法包含了化学物质(即食盐)的使用。故选B。
单选题 Why are many people against the use of chemicals to preserve food?
【正确答案】 C
【答案解析】事实细节题。根据文章最后一段最后两句可知，人们反对使用化学物质来保存食物的原因是“these chemicals may harm people if．．．”，C项是其同义转述。故选C。
单选题 What is the passage mainly about?
【正确答案】 A
【答案解析】主旨大意题。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、腌制法等。因此，文章的主旨是 保存食物的不同方法。故选A。