阅读下面短文并回答问题，然后将答案写在横线上（请注意问题后的词数要求）
[1] For the people living in the Nile Basin，the river is their life. This 6,825 km river，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.
[2] Water shortage，already serious in Egypt and Sudan，will soon influence several other countries in the watershed, too. 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 adds to the urgency.
[3] 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. Waterborne 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.
[4] 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 of water thickened with mud. They're very poor and have few choices.
[5] But a new program，the Nile Basin Initiative，is offering very practical assistance. The program is ________ a watermanagement project. It's a plan for the social and economic development of a vast district as well：it concentrates on the needs of the poorest of the poor and the environment that supports them.
[6] These are whole ecosystem problems，calling for united solutions．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.
小题1:What is the main idea of the second and third paragraphs? (No more than 10 words)
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小题2:Fill in the blanks in Paragraph 5 with proper words. (No more than 4 words)
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小题3:How large will the population of River Nile district be within the next 25 years?
(No more than 5 words)
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小题4:What do Nile Basin’s countries need to overcome the challenges? (No more than 6 words)
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小题5:What does the underlined word “Its” (Line 3, Paragraph 1 ) refer to?
(No more than 3 words)
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mgtgθ
mgsinθ
张力降低的变化。（）