using System;

using System.Linq;

using System.Threading.Tasks;

public class Program

{

    public static async Task Main()

    {

        var myStuff = new string[] {"A:1", "A:2", "A:3", "B:1", "B:2", "C:1", "C:2", "C:3", "C:4"};

        await Task.WhenAll(myStuff.Select(SomeMethodAsync));

    }

    static Random r = new Random();

    public static async Task SomeMethodAsync(string s)

    {

        var delay = r.Next(3000);

        await Task.Delay(delay);

        Console.WriteLine(s);

    }

}