有如下程序代码: #include using namespace std; class Square { public: Square(double _width = 0.0): width(_width) { } virtual double area() const { return width*width; } protected: double width; }; class Cube: public Square { public: Cube(double _width): Square(_width) { } double area() const { return width*width*width; } }; int main() { Cube a(10); Square &b = a; Square c = a; cout< return 0; } 则程序执行后的输出结果为 ( )