Hurt, R. Douglas
Garland Publishing, 1994
Buku Referensi
Kemp, Herman C.
KITLV Press, 1990
Buku Referensi
Vanessa Bainbridge ... [et al.]
International Institute for Environment and Development, 2000
Buku Teks
Groenendael, Victoria M. Clara van
Foris Publications, 1987
Buku Referensi
Freedman, Ronald
Irvington, 1975
Buku Teks