by Drs. Ibnu Syamsi, S.U $6.00
by Prof. Dr. Sondang P. Siagian, M.P.A $11.00
by Steven Dowsen, dkk $12.00
by Reni Dwi Purnomowati $11.00
by Baum, Warren C & Stokes M. Tolbert $7.00
by ML. Stein $6.00