Gianakaris, C. J., 1934-, author
Macmillan, 1992
Buku Teks
Shaffer, Peter
Longmans, 1973
Buku Teks
Shaffer, Thomas L.
West Publishing Company, 1976
Buku Teks
Shaffer, Thomas L.
West Publishing, 1987
Buku Teks
Steele, Peter, author
Oxford University , 1992
Buku Teks