阅读该程序，给出程序的输出结果。
#include <iostream.h>
class B
{
public:
virtual void fun1()
{
cout<<"B::fun1().\n";
}
virtual void fun2()
{
cout<<"B::fun2().\n";
}
void fun3()
{
cout<<"B::fun3().\n";
}
void fun4()
{
cout<<"B::fun4().\n";
}
};
class D:public B
{
public:
void fun1()
{
cout<<"D::fun1().\n";
}
void fun2()
{
cout<<"D::fun2().\n";
}
void fun3()
{
cout<<"D::fun3().\n";
}
void fun4()
{
cout<<"D::fun4().\n";
}
};
void main()
{
B *pb;
D d;
pb=&d;
pb->fun1();
pb->fun2();
pb->fun3();
pb->fun4();
}
