Merchant, John
Routledge, 2012
Buku Teks SO
edited by Roberto Walter Dal Negro and Richard Hodder
Springer, 2012
eBooks
Riley E. Dunlap ... et all, editor
Rowman & Littlefield Publishers, INC, 2001
Buku Teks
editors, Olen Gunnlaugson, Charles Baron, Mario Cayer
Igi Global, 2014
Buku Teks
Blake, Robert R.
Gulf Pub. Co., Book Division, 1978
Buku Teks SO