关于多态很继承的一个题目。求教

public class A{
public virtual void Fun1(int i){
conslole.Writeline(i);
}
public void Fun2(A a){
a.Fun1(i);
Fun(5);
}
}
public class B:A{
public override void Fun1(int i){
base.Fun1(i+1);
}
public static void Main(){
B b=new B();
A a=new A();
b.Fun2(a);
}
}