Scientists have developed a water treatment system that they say is a powerful but way to save lives. Four grams of chemicals can treat ten liters of dirty water for a low cost, about ten cents. Experts say infections from dirty water kill several thousand children in developing countries every day. The Procter and Gamble company has been developing the 'PUR Purifier of Water' system since 1995. The company has been working with the United States Centers for Disease control and Prion(C.D.C.). C.D.C. researchers tested it in Guatemala, Pakistan and Kenya. Procter and Gamble researcher Greg Allgood says cases of diarrhea(腹泻) in those studies fell by about 50 percent. Researchers from Johns Hopkins University in Maryland tested the system at a refugee camp in Liberia. Mr. Allgood says that study found a reduction of more than 90 percent. Use of the system is being expanded worldwide. The treatment contains bleach(漂白剂) to kill disease-causing organisms. It also contains something that dirt and other particles stick to. Mr. Allgood says the chemicals can remove lead and other erous metals and even agricultural poisons like D.D.T. Mr. Allgood heads the Children's Safe Drinking Water program at Procter and Gamble. He says about forty million packets of the treatment have been given to countries for free. They have been used in emergencies and in areas with limited supplies of clean water. Clean water is a limited resource in many parts of the world. Delegates from about 130 nations attended the Fourth World Water Forum last month in Mexico City. Scientists, policy experts and others discussed ways to provide clean water to the world’s poor. Organizers say more than twenty percent of the world population lacks clean drinking water. The final declaration did not go so far as to declare water a human right. But it did say that governments, not private companies, must take the lead in improving the public’s ability to have clean water. 46. What is mainly talked about in this passage? A. Water pollution around the world. B. The causes of diarrhea in African countries. C. A newly developed water treatment system. D. The Fourth World Water Forum in Mexico City. 47. Which of the following developed the water treatment system? A. The US Centers for Disease Control and Prion. B. The Procter and Gamble Company and C.D.C. C. The Children’s Safe Drinking Water Program. D. Johns Hopkins University. 48. Which of the following about the new water treatment system is NOT true? A. It is effective but very expensive. B. It was tested in Guatemala, Pakistan and Kenya. C. It is being expanded worldwide. D. It can remove erous metals in the water. 49. Which of the following shows that the shortage of clean water is a serious problem? A. Forty million packets of the treatment have been given to countries for free. B. Delegates from about 130 nations attended the Fourth World Water Forum. C. Four grams of chemicals can treat liters of dirty water for a low cost. D. Infections from dirty water kill several thousand children every day. 50. The best title for this article is ______. A. A Small Packet of Chemicals, a Big Effect on Dirty Water B. The Procter and Gamble Company and C.D.C. C. The Shortage of Clean Water D. How to Cure Diarrhea