using System;

public class Program

{

    public class A

    {

        public string p => "yea";

    }

    public class B

    {

        public A ap {get; set;}

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var test = new B(){ ap = null };

        //Console.WriteLine(test?.ap?.p);

        Console.WriteLine(test?.ap.p);

        Console.ReadLine();

    }

}