다음 글의 제목으로 가장 적절한 것은? Crops that are genetically modified (GM) have genes artificially added to them. These genes work in two ways. First, they make the crops resistant to weed killers. This means that farmers can spray all of their plants with poison, but the weeds will die and the crops will not. Secondly, the added gene or genes are designed to make the crop deadly to any pests that eat them, while being harmless to humans. Yet the use of GM crops is becoming controversial. Research has discovered that GM crops were harming the monarch butterfly, and also that GM food slowed growth and increased disease in rats. Opposition to genetically modified foods around the world is growing.