According to Article 20 of the Mediation Law, only Turkish citizens, who are graduates of law faculties, and who possess at least five year experience in his/her profession, may be a mediator. The mediator shall also have full capacity, not be condemned due to an intentional crime, and finish the mediation training and pass the written exam to be conducted by the Ministry of Justice. In order to be a mediator, one has to be registered as a mediator in the relevant central registry. Therefore, the correct option is A.