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。

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＞

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;

}

}

};