using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        List<string> strs = new List<string>{

            "a"

            ,"b"

            ,"c"

            ,"d"

            ,"e"

            ,"f"

        };

        var result = from s in strs

             where strs.IndexOf(s) % 2 == 0

             select s;

        Console.WriteLine(string.Join(",",strs));

        Console.WriteLine(string.Join(",",result));

        Console.WriteLine();

        string[] strary = strs.ToArray();

        Console.WriteLine(string.Join("$", strary));

        Console.WriteLine(string.Join("$", strary, 2,3));

        Console.WriteLine();

    }

}