why i generate instance outside of class. i give inheritance snifC to sinifD i need to create instance sinifC sinifc= new sinifC() in SinifD out side of constructor?

  public  class sinifC
    {
       public  void method3()
        {
            Console.WriteLine("Deneme3");
        }
    }

   public class sinifD : sinifC
    {
        void method4()
        {
            Console.WriteLine("Deneme4");
        }

        public sinifD()
        {
            sinifC sinifc = new sinifC();
            sinifc.method3();
        }
    }

i want to make it below:

    public  class sinifC
    {
       public  void method3()
        {
            Console.WriteLine("Deneme3");
        }
    }

   public class sinifD : sinifC
    {
        void method4()
        {
            Console.WriteLine("Deneme4");
        }


            sinifC sinifc = new sinifC();
            sinifc.method3();

    }

Error: Invalid token '(' in class, struct, or interface member declaration