XML : How to read namespace in a XML?

I am unable to read the namespace in a XML file. I need the value Id and store that in a string variable.

  <?xml version="1.0" encoding="UTF-8"?>  <tns:Connectionpoint xmlns:p="http://www.abc.be/abc/Data" xsi:Location="http://www.ABC.be/abc/ABC/MYFILE Managet.MYFILE.xsd ">  <Connection>  <ABC>    <XYZ>      <PQR>       <Id>DUMMY</Id>       <EndTime>2015-08-01112:00:00</EndTime>       <StartTime>2015-07-01112:00:00</StartTime>      </PQR>    </XYZ>  </ABC>    

I have tried the following way

  XmlDocument doc = new XmlDocument();   doc.Load(@"C:\Users\t.mahidharreddy\Desktop\ABC.xml");    XmlNode node = doc.SelectSingleNode("/tns:Connection/ABC/XYZ/PQR/Id");  string Id = node.InnerText;    

I am getting the following error:

Namespace Manager or XsltContext needed. This query has a prefix, variable, or user-defined function.