//引入命名空间
using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Xml;
using System.Xml.Linq;
public class MainClass {
    public static void Main() {
        XDocument xDocument = new XDocument(
          new XElement("Books",
            new XElement("Book",
              new XAttribute("type", "Author"),
              new XElement("FirstName", "J"),
              new XElement("LastName", "R"))));

        xDocument.Element("Books").Add(
          new XElement("Book",
            new XAttribute("type", "Author"),
            new XElement("FirstName", "E"),
            new XElement("LastName", "B")));

        xDocument.Element("Books").
          Element("Book").AddAfterSelf(
            new XElement("Book",
              new XAttribute("type", "Reviewer"),
              new XElement("FirstName", "F"),
              new XElement("LastName", "F")));

        Console.WriteLine(xDocument);
    }
}