学习多态的虚函数例子

class person
{
    public virtual void sayhello()
    {

    }
}

class chinese:person
{
    public overide void sayhello()
  
    {
    }

}

class Japanese:person
{
   public overide void sayhello()
  
    {
    }
}

class American:person
{
   public overide void sayhello()
  
    {