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บทสนทนานี้ใช้ตอบคำถามข้อที่ 51 - 55

          No matter where you live or when you were born, you almost surely have at least a small amount of DDT stored in the fatty tissues of your body. Why? This notorious toxic pesticide, which led to the extinction of the American bald eagle in 1970s, has long been banned in the U.S. and most other developed countries. But according to a new report by the World Wildlife Fund in Washington, DDT is still used in many developing nations, mainly because it’s so effective in controlling mosquitoes that carry the malaria parasite.

         The persistence of DDT is a problem—and not just in the countries that use it. DDT and several other common chlorine-containing pesticides are sturdy molecules that can stay intact for decades. They evaporate into the atmosphere and are blown by the wind all over the globe. They condense and fall to the ground in cold weather, especially in higher altitudes. Some of the highest concentrations of DDT are found in polar bears, penguins and the Inuit people of northern Canada.

          Although levels of DDT contamination are gradually falling in countries where the pesticide has been banned, new scientific research suggests that the chemicals are still a serious threat everywhere. Studies show that even small amounts of pesticides can disrupt the working of human hormones, interfering with reproduction and the functioning of the immune system. That’s why representatives of more than 100 nations gathered at a U.N. meeting in Nairobi to work toward a global treaty that would phase out DDT and 11 other pesticides, known as the “dirty dozen.” Environmentalists say it’s possible to find alternative way to fight malaria—and get rid of DDT once and for all.

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ข้อ 51
51 of 60
น้องๆ สามารถเลือกทำโจทย์ได้ตามต้องการ ไม่มีการจับเวลา ไม่มีการนับคะแนน ตอบผิดแล้ว สามารถตอบใหม่ได้ สิ่งสำคัญ ก็คือ ควรทำความเข้าใจกับวิธีทำในเฉลยละเอียด การเรียนคณิตศาสตร์ให้ได้คะแนนดี ต้องเรียนด้วยการลองทำโจทย์เยอะๆ
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