First Author:   Cyrille Dominick Bitting University of Bertoua bittingcyrille@gmail.com   Yaoundé, Cameroon   +237691865757(Phone) +237691865757(Fax) Second Author: Magloire Georges Sémé University of Yaoundé 2 magloireseme635@gmail.com         Third Author: Henri Ngoa Tabi University of Yaoundé 2 ngoa_henri@yahoo.fr