有如下程序: #include＜iostream＞ using namespace std; class Complex {double re, im; public:Complex(double r, double i): re(r), im(i) {}double real() const { return re; }double image() const { return im; }Complex& operator+= (Complex a){ re += a.re; im += a.im; return *this;} };ostream& operator＜＜(ostream& s, const Complex& z) { remm s＜＜’(’＜＜z.real()＜＜’,’＜＜z.image()＜＜’)’; } int main() { Complex x(1,-2), y(2,3);cout＜＜(x+=y)＜＜endl;return 0; } 执行这个程序的输出结果是
A．(1,-2)
B．(2,3)
C．(3,5)
D．(3,1)