有下列程序： #include＜iostream＞ using namespace std; class Complex { double re,im; public: Complex(double r,double i):re(r),im(i){} double real()const{retum 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) { return s＜＜’(’＜＜z.real()《’,’＜＜Z.image0＜＜’)’; } 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)