题目

    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 yeas ,the district's population is expected to double, adding to the demand圆（x+2）2+y2=5关于原点（0，0）对称的圆的标准方程为________．