Emerald Publishing, 2019
eBooks
Dobson, K.
Macmillan, 1975
Buku Teks SO
John Sikula, senior editor ; Thomas Buttery, editor, Edith Guyton, editor
Macmillan Library Reference USA, 1996
Buku Referensi
Adams, Anthony
Falmer Press, 1995
Buku Teks
Justin Dillon, Meg Maguire, editor
McGraw-Hill, 2011
Buku Teks