Method invocation using LINQ

List<ABC> abc = new List<ABC>()
           {
               new ABC { a = "YYY", b = "rrrr" },
               new ABC { a = "www", b = "ddd" }
           };

          //not working
           string result= abc.ForEach(a => ABC.MyMethod(a.b));
           //working
          var result1= abc.Select(a => ABC.MyMethod(a.b)).ToList();

public static string MyMethod(string input)
       {
           var c = input;
           return c;
       }