关于override和new在孙子类里面调用祖父类方法差异的问题

using System;
namespace foreachtest
{
    class program
    {
        public static void Main(string[] args)
        {
            A a=new A();
            B b=new B();
            A ab=new B();
            C c=new C();
//            a.afuc();
//            a.avfuc();
//            b.afuc();
//            b.avfuc();
//            ab.afuc();
//            ab.avfuc();
//            c.afuc();
            c.avfuc();
        }
    }
    class A
    {
        public void afuc()
        {
            Console.WriteLine("这是A的普通方法");
        }
        public virtual void avfuc()
        {
            Console.WriteLine("这是A的虚方法");
        }
    }
    class B:A
    {
        public new void afuc()
        {
            Console.WriteLine("这是B的普通方法");
        }
        public override void avfuc()
        {
//            base.avfuc();
            Console.WriteLine("这是B的虚方法");
        }
    }
    class C:B
    {
        public override void avfuc()
        {
            ((A)this).avfuc();//这里的问题
            Console.WriteLine("这是C的虚方法");
        }
        public new void afuc()
        {
            ((A)this).afuc();
            Console.WriteLine("这是c的普通方法");
        }
      

    }
}