C++ quiz. What independent changes will allow the code to wo

What independent changes will allow the code to work correctly?

class Counter {
  public: // 1
    void Count(); // 2
};

int main() {
  Counter obj;
  obj.Count();
  return 0;
}

// 3

Explanation

Let's consider all options one by one:

code couldn't compile without changes: obj.Count() calls function that doesn't have definition
changing private to public in line 1 wouldn't solve problems described above, but also we can't call private member of class
add code in line 3 also wouldn't solve first problem, class method still doesn't have definition