The Reader's Digest Association, Inc, 1998
Buku Teks SO
Bulechek, Gloria M.
WB Saunder, 1999
Buku Teks SO
Gallant, Ann
Stanley Thornes (Publishers) Ltd., 1992
Buku Teks SO
Ganderton, Lucinda
Hongkong : Page One Publishing, 2002,
Buku Referensi
Ganderton, Lucinda
Page One, 2002
Buku Referensi