阅读理解。 For the people living in the Nile Basin, the river is their life. This 6 825 km waterway, whose watershed (流域) covers three million square kilometers, flows through mountains, woodlands, lakes and deserts. Its potential for fishing, tourism and shipping is great-but so are its challenges. Water shortage already serious in Egypt and Sudan, will soon influence several other countries in the watershed as well. Today, about 160 million people depend on the Nile River for their living. Within the next 25 years, the district's population is expected to double, adding to the demand brought about by growth in industry and agriculture. The frequent drought (干旱) adds to the urgency. Water quality is also a problem Precious soil is washed out to sea. Wastes from industry and agriculture create pollution. Higher concentrations of salt influence irrigated soils. Water-borne diseases continue unchecked. In areas where it's hot and damp, water hyacinths choke off lakes, dams and other sections of the river, making it difficult for fishing and other businesses to move forward. Native people along the narrow area of farmland have watched the sand move closer day by day. They've seen the river change course, and their only source (来源) of water thickened with mud. They're very poor and have few choices. But a new program, the Nile Basin Initiative (NBI), is offering very practical assistance. The program is more than just a water-management project. It's a plan for the social and economic development of a vast district: it concentrates on the needs of the poorest of the poor and the environment that supports them. These are whole ecosystem problems, calling for united solutions (解决办法). Half the Nile Basin's countries are among the world's poorest nations; yet, somehow, they must find the resources, skills and political will to overcome these challenges. 1. What are the great challenges the Nile Basin faces? [     ] A. The development of shipping industry. B. Overfishing of native people. C. Water shortage and water quality. D. Increasing population and tourism. 2. The underlined word 'hyacinths' (in Paragraph 3) refers to '_____'. [     ] A. animals B. plants C. rocks D. salts 3. The program NBI is mainly aimed at _____. [     ] A. preventing water pollution B. changing the river course C. improving living conditions of the poor D. preventing land from becoming desert 4. What would be the best title of this passage? [     ] A. People's Life in Egypt and Sudan B. Frequent Drought in Egypt and Sudan C. The Poorest Countries in the Nile Basin D. The Ecosystem Problems in the Nile Basin