使用XPath读取xml

我有这个XML:

<?xml version="1.0" encoding="utf-8" ?>
<bookstore>
  <book id="ISBN-NUMBER">
    <title>
      The Autobiography of Benjamin Franklin
    </title>
    <author type="major">
      <first-name>
        Benjamin
      </first-name>
      <last-name>
        Franklin
      </last-name>
    </author>
    <price>
      8.99
    </price>
  </book>
  <book id="ISBN-NUMBER">
    <title>
      The Confidence Man
    </title>
    <author type="major">
      <first-name>
        Herman
      </first-name>
      <last-name>
        Melville
      </last-name>
    </author>
    <price>
      11.99
    </price>
  </book>
  <book id="ISBN-NUMBER">
    <title>
      The Gorgias
    </title>
    <author type="major">
      <name>
        Plato
      </name>
    </author>
    <price>
      9.99
    </price>
  </book>
</bookstore>

如何使用XPath读取它？我使用过：

XPathDocument doc = new XPathDocument(stream);
XPathNavigator nav = doc.CreateNavigator();
XPathNodeIterator node = nav.Select("bookstore/book");
while (node.MoveNext())

但是我该如何离开这里呢？如果节点是title、author和price，我想我需要一个swtich语句来swtich。如果是书，那么我需要阅读图书id，与作者和类型相同。