C＃中指定块内的XmlDocumentGetElementsByTagName

您没有使用Linq to XML：

var doc = XDocument.Load("data.xml");

var bookNodes = doc.Descendants("book").Where(b=> b.Parent.Name == "shop");

使用常规的System.Xml：

var doc = new XmlDocument();
doc.Load("data.xml");
var bookNodes = doc.SelectNodes(@"//bookstore/book");
foreach (XmlNode item in bookNodes)
{
    string title = item.SelectSingleNode("./title").InnerText;
    string price = item.SelectSingleNode("./price").InnerText;
    Console.WriteLine("title {0} price: {1}",title,price); //just for demo
}