Which of the following does the writer conclude at the end?
1 DDT is the most effective chemical in controlling mosquitoes that carry the malaria parasite
2 a small amount of pesticides can disrupt the working of both human hormone and immune system
3 the molecules of DDT and several other common chorine-containing pesticides
4 a global treaty that would phase out DDT and a other toxic peaticides should be enactes very soon