求大神指教，菜鸟感激不尽！

#include

using namespace std;
class A
{
public:
virtual void fun1()
{
cout<<"Class A1\t";
}
virtual void fun2(float x=0)
{
cout<<"Class A2\n";
}
};
class B:public A
{
public:
virtual void fun1()
{
cout<<"Class B1\t";
}
virtual void fun2(int x=0)
{
cout<<"Class B2\n";
}
};
class C:public B
{
public:
virtual void fun1()
{
cout<<"Class B4:\t";
}
virtual void fun2()
{
cout<<"Class B3\n";
}
};
int main()
{
A *pa;
B *pb;
C c;
pa=&c;
pa->fun1();
pa->fun2();
pb=&c;
pb->fun1();
pb->fun2();
return 0;
}
分析一下该程序的输出