Firth, Raymond
The New American Library, 1958
Buku Teks SO
Dolgoff, Ralph
Thomson Brooks/Cole, 2012
Buku Teks SO
Moody, Paul E.
McGraw-Hill, 1983
Buku Teks SO
Organisation for Economic Co-operation and Development, 1986
Buku Teks
edited by Egbert Jahn
St Martin's Press, 1978
Buku Teks SO