Read the following passage and choose the most likely answer to each of the following questions.
The food we eat seems to have profound effects on our health. Although science has made enormous steps in making food more fit to eat, it has, at the same time, made many foods unfit to eat. Some research has shown that perhaps eighty percent of all human illnesses are related to diet and forty percent of cancer is related to the diet as well, especially cancer of the colon. Different cultures are prone to contract certain illnesses because of the food that is characteristic in these cultures. That food is related to illness is not a new discovery. In 1945, government researchers realized that nitrates (硝酸钾) and nitrites (亚硝酸盐), commonly used to preserve color in meats, and other food additives, caused cancer. Yet, these carcinogenic additives remain in our food, and it becomes more difficult all the time to know which things on the packaging labels of processed food are helpful or harmful. The additives which we eat are not all so direct. Farmers often give penicillin to beef and poultry and because of this, penicillin has been found in the milk of treated cows. Sometimes similar drugs are administered (given) to animals not for medicinal purposes, but for financial reasons. The farmers are simply trying to fatten the animals in order to obtain a higher price on the market. Although the Food and Drug Administration has tried repeatedly to control these procedures, the practices continue.
What are nitrates used for?（ ）.
A、
They preserve flavor in packaged foods
B、
They preserve the color of meats
C、
They are the objects of research
D、
They cause the animals to become fatter
【正确答案】：B
【题目解析】：
本题考查亚硝酸盐的用处。
定位到第六句“1945年，政府研究人员意识到通常用于保存肉类颜色的硝酸盐和亚硝酸盐，以及其他食品添加剂可能导致癌症。”可知，B选项符合题意。