阅读下列C++程序说明，将应填入(n)处的字句写在对应栏内。 【说明】 以下C++程序的功能是计算三角形、矩形和正方形的面积并输出。4个类组成：类Triangle、Rectangle和Square分别表示三角形、矩形和正方形；抽象类Figure提供了一个纯虚拟函数getArea()，作为计算上述3种图形面积的通用接口。 include＜iostream.b＞ include＜math.h＞ class Figure{ public: virtual double getArea0=0; //纯虚拟函数 }; class Rectangle: (1) { protected: double height; double width; public: Rectangle(){}; Rectangle(double height, double width){ This-＞height=height; This-＞width=width; } double getarea(){ return (2); } }; class Square: (3) { public: Square(double width){ (4); } }; class Triangle: (5) { double la; double lb; double lc; public: Triangle(double la, double lb, double lc){ this-＞la=la; this-＞lb; this-＞lc; } double getArea(){ double s=(la+lb+lc)/2.0; return sqrt(s*(s-la)**(s-lb)*(s-lc)); } }; viod main(){ Figure* figures[3]={ new Triangle(2,3,3), new Rectangle(5,8), new Square(5)); for(int i=0;i＜3;i++){ cout＜＜'figures['＜＜i＜＜']area='＜＜(figures[i])-＞getarea()＜＜endl; } }