using System;

using System.Threading.Tasks;

​

namespace AsyncAwait

{

    public class A

    {

        public virtual void Hello()

        {

            Console.WriteLine("Hello A");

        }

    }

​

    public class B : A

    {

        public override void Hello()

        {

            Console.WriteLine("Hello B");

        }

    }

​

    public class C : B

    {

        public virtual new void Hello()

        {

            Console.WriteLine("Hello C");

        }

    }

​

    public class D : C

    {

        public override void Hello()

        {

            Console.WriteLine("Hello D");

        }

    }

​

    public class Program

    {

        public static async Task Main(string[] args)

        {

            A a = new A();

            a.Hello();

​

            A b = new B();

            b.Hello();

​

            A c = new C();

            c.Hello();

​

            A d = new D();

            d.Hello();

​

            C x = new C();

            x.Hello();

​

            C y = new D();

            y.Hello();

        }

    }

}