//initialize a dictionary with keys and values.    Dictionary<int, string> plants = new Dictionary<int, string>() {        {1,"Speckled Alder"},        {2,"Apple of Sodom"},        {3,"Hairy Bittercress"},        {4,"Pennsylvania Blackberry"},        {5,"Apple of Sodom"},        {6,"Water Birch"},        {7,"Meadow Cabbage"},        {8,"Water Birch"}    };  Response.Write("<b>dictionary elements........ www.1sucai.cn </b><br />"); //loop dictionary all elements   foreach (KeyValuePair<int, string> pair in plants)  {     Response.Write(pair.Key + "....."+ pair.Value+"<br />"); }  //find dictionary duplicate values.  var duplicateValues = plants.GroupBy(x => x.Value).Where(x => x.Count() > 1); Response.Write("<br /><b>dictionary duplicate values..........</b><br />"); //loop dictionary duplicate values only            foreach(var item in duplicateValues)  {     Response.Write(item.Key+"<br />"); }