Carpenter, Catrine
McGraw-Hill, 2004
Buku Teks SO
Bladon, Rachel
Passport Books, [Date of publication not identified]
Buku Teks SO
Coultas, Barbara
Teach Yourself Books, 1990
Buku Teks SO
Rybak, Stephanie
Macmillan, 1985
Buku Teks SO
Barratt, William B.
Aldine House, 1994
Buku Teks