Gant, George F.
University of Wisconsin Press, 1979
Buku Teks
DuBrin, Andrew J.
Pergamon Press, 1972
Buku Teks
Hayder, Joseph Ralston
Macmillan, 1950
Buku Teks
Abril-Ojeda, Galo
Institute of Latin American Studies , 1982
Buku Teks
Bingham, Robert C.
McGraw-Hill, 1987
Buku Teks