Ewles, Linda
Scutari Press, 1995
Buku Referensi
Rorden, Judith Waring
W.B. Saunders Company, 1987
Buku Teks SO
Dadzie, Stella
National Institute of Adult Continuing Education, 1993
Buku Teks
Jones, Andrew
Radcliffe Publishing, 2009
Buku Teks
Schriven, Angela
Elsevier, 2010
Buku Teks SO