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) { return s<<’(’<<z.real()<<’,’<<z.image()<<’)’; } int main() { Complex x(1,2),y(2,3); tout<<(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)