Edwards, Philip
British Council by Longmans, Green, 1970
Buku Teks SO
Canavan, P. Joseph
D.C. Health and Company, 1990
Buku Teks SO
edited by Richard T. de George
University of Kansas, 1981
Buku Teks SO
edited by Miguel de Beistegui, Simon Sparks
Routledge, 2000
Buku Teks SO
edited, Rebecca Bushnell
Blackwell Publishing, 2005
Buku Teks SO