试题六（共 15 分）阅读以下说明和C++程序代码，将应填入（n） 处的字句写在答题纸的对应栏内。[说明]在下面的C++代码中，类SalesTicket 能够完成打印票据正文的功能，类HeadDecorator 与FootDecorator 分别完成打印票据的台头和脚注的功能。已知该程序运行后的输出结果如下所示，请填补该程序代码中的空缺。这是票据的台头！这是票据正文！这是票据的脚注！------------------------这是票据的台头！这是票据的脚注！[C++程序代码]#include using namespace std;class SalesTicket {public:(1) printTicket() { cout << "这是票据正文!" << endl;}};class Decorator : public SalesTicket{SalesTicket *ticket;public:Decorator(SalesTicket *t){ ticket = t; }void printTicket(){if(ticket != NULL)ticket->printTicket();}};class HeadDecorator : public Decorator{public:HeadDecorator(SalesTicket *t): (2) { }void printTicket() {cout << "这是票据的台头！" << endl;Decorator::printTicket();}};class FootDecorator :public Decorator{public:FootDecorator(SalesTicket *t): (3) { }void printTicket() {Decorator::printTicket();cout << "这是票据的脚注！" << endl;}};void main(void) {SalesTicket t;FootDecorator f(&t);HeadDecorator h( (4) );h.printTicket();cout << "------------------------"<< endl;FootDecorator a(NULL);HeadDecorator b( (5) );b.printTicket();}