Bowman, Phil
Nelson, 1989
Buku Teks
Lugton, Robert C.
Prentice-Hall, 1978
Buku Teks
Hill, Robert J., author
Macmillan, 1982
Buku Referensi
Thomson, A.J., author
Oxford Oxford University Press, 1986
Buku Teks
Steinberg, Roberta, author
Prentice-Hall, 1987
Buku Teks