问答题

3. GM foods are good for the environment. The damage to the environment that insecticides, such as DDT, bring about is well known. The use of synthetic fertilizers on farmland leads to the eutrophication of rivers and lakes all over the world. GM foods use fewer pesticides, herbicides and fertilizers, and, therefore, cause less pollution. 该段涉及两类举例方法，一类是带有信号词的举例______，一类是隐形举例，即不含信号词_______。