单项选择题
A．they sell cars door-to-door B．they buy presents for their customers C．they enjoy themselves in recreation centers D．they go out to do market researches
A．Because of science, most of the foods we eat today are contaminated. B．It has caused a lack of information concerning the value of food. C．As a result of scientific intervention, some potentially harmful substances have been added to our food. D．The scientists have preserved the color of meats, but not of vegetables.
A．the attempt to fatten the animals B．the attempt to cure sick animals C．the using of drugs to animals D．the using of additives to preserve the color of food