Из задач на собеседование,
http://rsdn.ru/forum/job/6423376.1

Автор: mgu
Дата: 21.04.16

using System;
using System.Xml.Linq; // add System.Xml.Linq.dll to references
using System.Linq;

class MainClass
{
    public static void Main (string[] args)
    {
        // 
        var doc = XDocument.Parse(@"<ul>
                <li>Coffee</li>
                <li>Tea</li>
                <li>Milk</li>
                </ul>");
        var list = doc.Root.Elements("li")
            .Select(element => element.Value)
            .ToList();            
        var reversed_list = list.AsEnumerable().Reverse();
        XElement xmlElements = new XElement("ul", reversed_list.Select(i => new XElement("li", i)));
        System.Console.Write(xmlElements);
    }
}

http://stackoverflow.com/questions/1542073/xdocument-or-xmldocument
http://stackoverflow.com/questions/747554/populate-xdocument-from-string
http://stackoverflow.com/questions/956749/how-can-i-transform-xml-into-a-liststring-or-string
http://stackoverflow.com/questions/19102021/how-to-reverse-a-generic-list-without-changing-the-same-list
http://stackoverflow.com/questions/17043663/how-to-serialize-a-listt-into-xml


моё время решения — 40 минут