单选题
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.
单选题
How can we preserve food according to the first paragraph? ______
【正确答案】
C
【答案解析】 根据文章第一段第一句“To preserve food, the growth of bacteria must be controlled.”可知，为了保存食物，必须控制细菌的生长，故选C。
单选题
Cooking is an effective way in preserving food because ______.
【正确答案】
D
【答案解析】 根据第三段第一、二句“Cooking will usually kill bacteria...remove water, and this aids in preserving food.”可知，在一定的条件下烹饪法能杀死细菌，因此是一种保存食物的有效方法，故选D。
单选题
The method of salting food ______.
【正确答案】
B
【答案解析】 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。
单选题
Why are many people against the use of chemicals to preserve food? ______
【正确答案】
C
【答案解析】 根据最后一段最后两句“Some people oppose the use of chemicals in food. They say that these chemicals may harm people if the chemicals can harm bacteria.”可知，一些人反对使用化学物质来保存食物是因为他们认为化学物质可以消灭细菌的话，对人体也会有害，故选C。