Palmer, Robert Roswell, 1909-2002
McGraw-Hill, 1992
Buku Teks SO
Malchow, Howard L.
Bloomsbury Academic, an imprint of Bloomsbury Pub, 2016
Buku Teks SO
Cook, Chris
Longman, 1991
Buku Referensi
Stavrianos, Leften Stavros
Prentice-Hall, 1982
Buku Teks SO
Cook, Chris
Routledge, 2005
Buku Teks SO