煤层稳定性

有以下程序： #include ＜iostream＞ using namespace std; #define PI 3.14 class Point { private: int x,y; public: Point(int a,int b) {x=a;y=b; } int getx() {return x; }int gety() {return y; } }; class Circle: public Point {private:int r;public: Circle(int a, int b,int c):Point(a,b) {r=c; }int getr() {return r; } double area() {return PI*r*r; } }， int main() { Circle c1(5,7,10); cout＜＜c1 .area()＜＜endl; return0； } 程序执行后的输出结果是

A．314

B．157

C．78.5

D．153.86