迭代器实现时候程序无法继续执行怎么回事？

C# code

        static void Main(string[] args)        {            string Tem_str = "";             string str = "abcdefg"; //对str字符串逆序输出            foreach (object i in Transpose(str))            {                Tem_str += i.ToString();            }                      Console.WriteLine(Tem_str);                      Console.ReadKey();        }            public static IEnumerable<object> Transpose(string n)        {                           for (int i = n.Length - 1; i >= 0; i++)                {                    yield return (object)n[i];                }                  }