53. 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 chlorine-containing pesticides cannot be damaged for many years.
4. A global treaty that would phase out DDT and 11 other notorious toxic pesticides should be enacted very soon.