Parents' Magazine's Cultural Institute, 1965
Buku Referensi
Turner, Ralph
McGraw-Hill, 1941
Buku Teks
edited by S.L. Goldberg and F.B. Smith
Cambridge University Press, 1988
Buku Teks SO
Gilman, Sander L.
Polity Press, 2008
Buku Teks SO
Mohammed Ali
Punjab Eductional Press, 1964
Buku Teks