阅读以下说明和C++程序，将应填入(n)处的字句写在答题纸的对应栏内。
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。
程序由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＞
inclule ＜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-＞lb ='lb; this-＞lc = lc;
}
double getArea() {
double s = (la+lb+lc)/2.0;
return sqrt(s*(s-la)*(s-lb)*(s-lc));
} }; void main() {
Figure* figures[3] = {
new Triangle(2,3,3), new Rectangle(5,8), new Square(5)};
for (int i = 0; i ＜ 3; i++) {
com ＜＜ "figures[" ＜＜ i ＜＜ "] area =" ＜＜ (figures[i])-＞getArea0 ＜＜ endl;
}