Tivy, Joy, author
Longman Scientific & Technical, 1992
Buku Teks
Hanks, Lucien M
Aldine Atherton, 1972
Buku Teks
edited by Jose I. Furtado
Harwood Academic , 1990.
Buku Teks
Brewer, Richard, author
Saunders College Publishing, 1994
Buku Teks
Ehrlich, Paul R., author
Macmillan, 1987
Buku Teks