I dont think it would be possible for someone to listen to your calls im pretty sure only the police could if they provide a sign warrent by a judge to the phone company
Computer security is protection from theft or damage to their hardware, software, or information, as well as disruption or misdriection of the services they provide. As information security is the practice of preventing unauthorized access, use, disclosure, disruption, modification, inspection, recording, or destruction of information.
I think the answer is A. The classroom is a place for learning not for making phone calls