namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            B b = new B();
            A a = new A();
            A c = new B();
            b.Show();
            a.Show();
            c.Show();
            Console.Read();
        }
    }

    public class A
    {
        public void Show()
        {
            Console.WriteLine("执行A的Show方法");
        }

    }

    public class B : A
    {
        public void Show()
        {
            Console.WriteLine("执行B的Show方法");
        }
    }
}