Pred, Allan
Routledge, 1995
Buku Teks
Gelinas, Ulric J.
PWS-KENT Publishing Company, 1990
Buku Teks
Beals, Alan R.
Holt, Rinehart and Winston, 1967
Buku Teks
O`Brien, James A., 1936-
McGraw-Hill, 2003
Buku Teks
O`Brien, James A., 1936-
McGraw-Hill, 2002
Buku Teks