Protected поле - C#

{
    class Program
    {
        static void Main(string[] args)
        {
            Derivative D=new Derivative(6);
            D.T=new Test(5);       
            D.T.Write();
            D.Write();
            Console.ReadLine();
        }
    }
 
    class Test
    {
        public int x;
        protected int y;
        private int z;
        public Test (int Y)
        {
            y = Y;
        }
        public void Write()
        {
          Console.WriteLine(  this.y);
        }
    }
    class Derivative:Test
    {
        public Test T;
        public Derivative(int x ):base(x)
        {
         // T.y=10;   не дает обратиться 
            
        }
        
    }
}