单项选择题

Task 1
Directions: After reading the following passage, you will, find 5 questions or unfinished statements numbered 36 to 40. For each question or statement there are 4 choices marked A), B), C) and D). You should make the correct choice and mark the corresponding letter on the Answer Sheet with a single line through the center.

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.

Cooking is an effective way in preserving foods because .