有以下程序#include＜iostream＞using namespace std；class Complex{public：Complex(double r=O,double i＝0)：re(r),im(i){}double real() const {return re；}double imag()const {return im；}Complex operator ＋(Complex C) const{return Complex (re＋c.re,im＋c.im)；}private：double re,im；}；int main(){Complex a=Complex(1，1)＋Complex (5)；cout＜＜a.real()＜＜’’＋’’＜＜a.imag()＜＜’’i’’＜＜endl；retum 0；}程序执行后的输出结果是【 】
A．6＋6i
B．6＋1i
C．1＋6i
D．1＋1i