阅读以下说明和C++程序，将应填入(n)处的字句写在对应栏内 [说明] 以下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()，作为计算上述三种图形面积的通用接口。 [C++程序] include＜iostream.h＞ include＜math.h＞ class Figure{ public: virtual double getArea()=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-＞ib;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)-＞getarea()＜＜endl; } } };