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正方体、球体和圆柱体的表面积和体积并输出。 4个类组成：类cube、sphere和cylinder分别表示正方体、球体和圆柱体；抽象类 container为抽象类，提供了两个纯虚拟函数surface_area()和volum()，作为通用接口。 【C++程序】 include＜iostream.h＞ define pi 3.1416 class container｛ protected: double radius; public: container(double radius) {container::radius=radius;} virtual double surface_area()=0; virtual double velum()=0; }; class cube:(1){ //定义正方体类 public: cube(double radius):container(radius){}; double surface_area () {return 6 * radius * radius;} double volum() {return radius * radius * radius;} }; class sphere:(2){ //定义球体类 public: sphere(double radius): container(radius){}; double surface_area() { return (3);} double volum() {return pi * radius * radius * radius * 4/3;} }; class cylinder:(4){ //定义圆柱体类 double height; public: cylinder(double radius,double height):container(radius) { container::height=height; } double surface_are a () { return 2 * pi * radius * (height+radius); } double volum () {return (5);} }; void main() { container * p; cube obj1 (5); sphere obj2(5); cylinder obj3(5,5); p=&obj1; cout＜＜“正方体表面积”(＜＜p-＞surface_area()＜＜end1; cont＜＜“正方体体积”＜＜p-＞volume()＜＜end1; p=&obj2; cout＜＜“球体表面积”＜＜p-＞surface_area()＜＜end1; cout＜＜“球体体积”＜＜p-＞volume()＜＜end1; p=&obj3; cout＜＜“球体表面积”＜＜p-＞surface_area()＜＜end1; cout＜＜“球体体积”＜＜p-＞volume()＜＜end1; }