A、Which food could be sold. B、How foods must be described. C、When certain foods are available. D、What nutrients food should cont

Until recently, a tomato was just a tomato.[20]But now scientists have begun to change the genes of plants in biology laboratories. So now it is not as easy to know whether tomatoes you eat are pure tomatoes. That is true with many other vegetables and fruits people could find on the market.
    Genetic engineering is the process of taking genes from one plant or animal and putting them into an other plant or animal. Scientists use the process to increase the nutrients a food contains. However, this new genetic engineering technology has raised a lot of questions among people.
    The United States Food and Drug Administration(FDA)is responsible for deciding how foods must be described when they are sold to the customers. The FDA says people who buy human foods produced by new kinds of plants must be told if there are any safety problems. It also says people must be told what nutrients the foods contain.
    There are, however, times when more information about a new food product would be helpful to certain people. Some foods are not a safety threat, but do bring effects to people in unusual ways. For example,[22]after eating the food, they may develop red spots on their skin in a few hours, or have trouble in breathing or have a sick stomach.
20. In what way might fruits and vegetables nowadays be different from those before?
21. What is the FDA responsible for deciding?
22. What may happen to people after eating certain food?