edited by Norman MacKenzie
The New American Library, 1968
Buku Teks SO
Pratt, Vernon
Methuen, 1978
Buku Teks SO
Mouton, Jane S.
Hague, 1968
Buku Teks SO
edited by Bert F. Hoselitz
Free Press, 1959
Buku Teks SO
United Nations Educational, Scientific and Cultural Organization (UNESCO)
UNESCO, 1984
Buku Teks SO