using System;

using System.Linq;

using System.Threading.Tasks;

​

public class Program

{

    public static void Main()

    {

        Task.Run(async () =>

        {

            await StartTask();

        }).Wait();  

    }

    public static async Task StartTask(){

        var tasks = Enumerable.Range(0, 9).Select(async x => await Delay(x)).ToList();

        Console.WriteLine("More results below to show concurrent");

        await Task.WhenAll(tasks.ToArray());

        Console.WriteLine("all tasks are done");

    }

​

    public static async Task<int> Delay(int x)

    {

        Console.WriteLine("a" + x);

        await Task.Delay(200 * (x + 1));

        Console.WriteLine(x);

        return x;

    }

}