First Author:   Melingui bate Adalbert Abraham Ghislain University of Dschang melibate@yahoo.fr   Dschang, 110, Dschang (Cameroon), Cameroun   +237676249644(Phone) +237676249644(Fax) Second Author: Avom Désiré University of Yaoundé 2 (Soa) davom99@gmail.com   Independence square Yaoundé, 1365, Yaoundé (Cameroon), Cameroun