Sweedlum, Verne S.
American Book Company, 1956
Buku Teks SO
Xu, Zhonglin
World Publishing House, 2000
Buku Teks
edited by Roger Penn, Damon Berridge
Sage, 2013
Buku Teks SO
Yeh, Ling-hsia
MA Cheng & TSui, 1994
Buku Teks
edited by Alan Bryman, Robert G. Burgess
SAGE Publication, 1999
Buku Teks SO