Storing child class objects in a List of base class

abstract class A

    {

        public abstract void diap();

    }

    class B:A

    {

        public override void diap()

        {

            Console.WriteLine("B");

           

        }

    }

    class C:B

    {

        public override void diap()

        {

            Console.WriteLine("C");

            base.diap();

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            List<A> li = new List<A>();

            B obj1 = new B();

            C obj2 = new C();

            li.Add(obj1);

            li.Add(obj2);

           

            foreach(A ob in li)

            {

                ob.diap();

            }

            Console.ReadLine();

        }

    }

Output - 

B

C

B