Allen L. Hammond [and others]
Oxford University Press , 1996
Buku Teks
Gerald Segal
Simon and Schuster, 1996
Buku Referensi
D.C. The World Bank , 1994
Buku Teks
De Blij, Harm J., author
John Wiley & Sons, 1993
Buku Teks
Penna, Anthony N, author
Blackwell, 2013
Buku Teks