class Program

    {

        static void Main(string[] args)

        {

           // 输出 ypoc si yek eht

            string str = "the key is copy";

            char[] arr = str.ToCharArray();

            Array.Reverse(arr);

            var result = new string(arr);

           //输出 copy is key the

            string[] ss = str.Split(new string[] { " " }, StringSplitOptions.None);

            var resilt = ss.Reverse();

            var temp = String.Join(" ", resilt);

            Console.WriteLine(temp);

            Console.ReadKey();

        }

    }