完成下面程序中的show函数的定义，使其运行结果如下： In base In derived程序清单如下： #include using namespace std; class base { pubhc : virtual void print( ) { cout << "In base" << endl; } }; class derived: public base { public : void print( ) { cout << "In derived" << endl; } }; void show(base * pb,void (base:: * pf) ( ) ) { _________ } void main( ) { base b; derived d ; show ( &b, base::print); show ( &d, base::print); }