by Robert K. Cooper, Ph.D. Ayman Sawaf $13.00
by Dr. Achmad S. Ruky $11.00
by Prof. Dr. Sondang P. Siagian, M.P.A $7.00
by Ali Masjono Mukhtar, S.E., M.Bit $7.00
by $7.00
by Sanusi, Bachrawi $6.00