using System;

using System.Collections.Generic;

​

public class Program

{

    public class AData

    {

        public int x = 42;

    }

    public class A

    {

        public AData data {get;set;} = new AData();

    }

    public class BData: AData

    {

        public int y = 12;

    }

    public class B: A

    {

        public BData data {get;set;} = new BData();

    }

    public static class fun{

        public static void myfunc(AData someData)

        {

            Console.WriteLine(someData.x);

        }

    }

    public static void Main()

    {

        var obj = new B();

        fun.myfunc(obj.data);

    }

}