Smyth, Angela
Thorsons, 1994
Buku Referensi
Hebert, David
Avery Pub. Group, 1998
Buku Teks SO
Lu, Henry C.
Black Dog & Leventhal Publishing, Inc, 1999
Buku Teks SO
Elliot, Rose
Chapmans Publisher Ltd., 1994
Buku Referensi
Geddes & Grsset, 1997
Buku Teks SO