public static void Main()
string s = "<div class=\"hidden-xs hidden-sm\"><div class=\"related-article\"><a class=\"clearfix\" href=\"/Articles/Details?Guid=26e935b9-ee13-4847-bc43-46c109c94aeb&CatId=1\"><img src=\"https://www.taiwan-panorama.com/Uploads/2017/03/006/01.jpg?w=300\" alt=\"\"><h3 class=\"related-title col-md-12\">天使,跨國越境傳愛</h3><p class=\"hidden-xs related-content col-xs-12\"><span class=\"more-2\">...more</span></p></a></div></div>";
int start = s.IndexOf("<img");
s=s.Insert(start,"<div class=\"kevin\">");
int end = s.IndexOf("<h3");
s=s.Insert(end,"</div>");