//父类
    class Person
    {
        public Person() { }

        public void Hi()
        {
            Console.WriteLine("  Excute  Person Hi()");
        }
    }

 //子类
    class Student:Person
    {
        public void Hi()
        {
            Console.WriteLine("Excute Student Hi()");
        }

    }

  //主方法
    class Program
    {
        static void Main(string[] args)
        {
            Person person = new Student();
            person.Hi();
        }
    }