public void DemoVanOverrideVanMethod()
{
Base b = new Base();
Derived d = new Derived();
Console.WriteLine(b.CalculateInterest(100m));
Console.WriteLine(d.CalculateInterest(100m));
}
public void DemoVanAbstractClass()
{
Abstract a = new Base();
Console.WriteLine(a.CalculateInterest(100m));
}