初学：返回xml字符串的处理问题？

返回如下xml字符串：
<?xml version="1.0" encoding="utf-8" ?>
<DeliverMsg xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="igw.zsdx.com">
  <returncode>0 </returncode>
  <msg/>
  <mos>
    <MO>
      <aaa>3150 </aaa>
      <bbb>1182760 </bbb>
      <ccc>07608888888 </ccc> 
    </MO>
    <MO>
      <aaa>3151 </aaa>
      <bbb>1182760 </bbb>
      <ccc>07608888888 </ccc> 
    </MO>
    <MO>
      <aaa>123 </aaa>
      <bbb>118276039 </bbb>
      <ccc>07608888888 </ccc> 
    </MO>
  </mos>
</DeliverMsg>

请教，如何获取各MO下aaa等属性的值？

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XmlDocument doc = new XmlDocument();
doc.Load("xml");
doc.SelectNodes("/DeliverMsg/mos/Mo");

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下面代码是在winform开发环境下.
C# code

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