public abstract class A {
   public string PublicPrint() { 
      return Print(); 
   } 
 
   protected virtual string Print() {
        return "A"; 
   } 
}
 public class B : A { } 
 public class C : B { 
     protected override string Print() { 
         return "C"; 
     } 
}
 

 
A ac = new C(); 
Console.WriteLine(ac.PublicPrint());