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", "A"),
new XElement("LastName", "B"))));
xDocument.Element("Books").Add(
new XElement("Book",
new XAttribute("type", "Author"),
new XElement("FirstName", "E"),
new XElement("LastName", "B")));
xDocument.Element("Books").
Elements("Book").
Where(e => ((string)e.Element("FirstName")) == "E").
Single().AddBeforeSelf(
new XElement("Book",
new XAttribute("type", "Reviewer"),
new XElement("FirstName", "F"),
new XElement("LastName", "F")));
Console.WriteLine(xDocument);
}
}