using System;

using System.Text;

​

public static class StringExtension

{

    public static string ReverseSentence(this string str)

    {

        //complete the implementation here      

        throw new NotImplementedException();

    }

}

​

public class Program

{

    public static void Main()

    {

        string str = "reverse this string";

        // Complete the implementation such that the str in reversed to 

        // string this reverse

        Console.WriteLine(str);

    }

}