Abril-Ojeda, Galo
Institute of Latin American Studies , 1982
Buku Teks
World Bank
Oxford University Press, 1988
Buku Teks
Golay, Frank H., author
Cornell University Press, 1961
Buku Teks
Pustaka Sinar Harapan, 1997
Buku Teks
Newman, Herbert E., author
John Wiley & Sons, 1968
Buku Teks