一个xml的问题

MainClass .cs
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using System;
using System.Windows.Forms;
using System.Xml;namespace all
{ public class MainClass
{
[STAThread]
static void Main() 
{
            XmlDocument doc = new System.Xml.XmlDocument();
           
            doc.Load("x.xml");
            XmlNamespaceManager manager1 = new XmlNamespaceManager(doc.NameTable);
            manager1.AddNamespace("Nikens", "http://www.nike.com");
            XmlNode node1 = doc.DocumentElement.SelectSingleNode("Nikens:Model", manager1);            if (node1 == null){
                Console.WriteLine("node1 is null");
              }            Console.WriteLine("Finish");
            Console.Read();
}
}
}
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x.xml
<?xml version="1.0" encoding="utf-8"?>
<Model xmlns="http://www.nike.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Class assembly="Datanike" type="Gove">

</Class>
</Model>
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