Townsend, Sue
Penguin , 2004
Buku Teks
Currance, Phillip L.
Elsevier , 2005
Buku Referensi
edited by Warren K. Agee, Phillip H. Ault, Edwin Emery
Harper and Row, 1982
Buku Teks
Fenner, M. Kathleen
D. Van Nostrand Comp., 1980
Buku Teks
Rampton, Sheldon
Penguin, 2003
Buku Teks