Garner, Hugh
Simon & Pierre Pub. Co., 1974
Buku Teks SO
by Ron Hamilton ... [and others]
University of Queensland, 1970
Buku Teks SO
Cassady, Marshall
National Textbook Company, 1994
Buku Teks SO
Hampden, John
J. M. Detn & Sons, 1956
Buku Teks SO
International labour office , 1988
Buku Teks SO