csharp_tutorial_1.cs

static List<string> GetAdLinks(string url){
   var mainPageAdLinks = new List<string>();
   var html = GetHtml(url);
   var links = html.CssSelect("a");

   foreach (var link in links){
       if(link.Attributes["href"].Value.Contains(".html")){
           mainPageAdLinks.Add(link.Attributes["href"].Value);
       }
   }
   return mainPageAdLinks;
}