Out of the choices given, B. Ask your manager beforehand what to do if the person being called is unavailable is the best answer so that the correct course of actions are taken. If you call and no one answers or even if they do, it's important to understand the correct way to handle the situation instead of being confused or doing the wrong thing. Once you've understood how your manager wants you to handle these situations, you are able to have better knowledge for future phone calls.