Which code, inserted at line 10, generates the output "2?

Which code, inserted at line 10, generates the output "2?1"?

#include

#include

using namespace std;

class A {

protected:

int y;

public:

int z;

};

//insert code here

public:

void set() {

y = 2;

z = 3;

}

void Print() { cout << y << z; }

};

int main () {

B b;

b.set();

b.z = ?1;

b.Print();

return 0;

}