What will be the output of the following C++ code?

#include <iostream>
using namespace std;
class Integer 
{
    int i;
    public:
    Integer(int ii) : i(ii) {}
    const Integer
    operator+(const Integer& rv) const 
    {
        cout << "operator+" << endl;
        return Integer(i + rv.i);
    }
    Integer&
    operator+=(const Integer& rv) 
    {
        cout << "operator+=" << endl;
        i += rv.i;
        return *this;
    }
};
int main() 
{
    int i = 1, j = 2, k = 3;
    k += i + j;
    Integer ii(1), jj(2), kk(3);
    kk += ii + jj;
}

A. operator+
operator+=

B. operator+=
operator+

C. operator+
operator+

D. operator+
operator=

Answer: Option A