请教如何设计接口（C#）?

interface IPrint {
  void Print();
}class A : IPrint {
  public void Print() {
    System.Console.WriteLine("A");
  }
}class B : IPrint {
  public void Print() {
    System.Console.WriteLine("B");
  }
}class AppMain {
  public static void Print(IPrint obj) {
    obj.Print();
  }
  public static void Main() {
    Print(new A()); // display A
    Print(new B()); // display B
  }
}